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NIST Special Publication 800-21

Guideline for Implementing Cryptography in the Federal

Government

November 1999

December 2005

SP 800-21 is superseded in its entirety by the publication of

SP 800-21 2nd edition (December 2005).

NIST Special Publication 800-21 2nd edition

Guideline for Implementing Cryptography in the Federal Government

Elaine B. Barker, William C. Barker, Annabelle Lee

December 2005

http://dx.doi.org/10.6028/NIST.SP.800-21e2

Computer Security Division (Information Technology Lab)

SP 800-21 2nd edition (as of June 19, 2015)

http://csrc.nist.gov/projects/crypto.html

N/A
NIST Special Publication 800-21

U.S. DEPARTMENT OF

COMMERCE

Technology Administration

National Institute of Standards

and Technology

Guideline for Implementing

Cryptography in the

Federal Government

NATL INST. OF STAND & JECH

AlllDb MDHSD3

WIST

PUBL/CAT/ONS

Annabelle Lee

COMPUTER SECURITY

QC

100

U57

.800-21

[999

Nisr
fhe National Institute of Standards and Technology was established in 1988 by Congress to "assist industry in the development of technology . . . needed to improve product quality, to modernize manufacturing processes, to ensure product reliability . . . and to facilitate rapid commercialization ... of products based on new scientific discoveries." NIST, originally founded as the National Bureau of Standards in 1901, works to strengthen U.S. industry's

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As an agency of the U.S. Commerce Department's Technology Administration, NIST conducts basic and

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'At Boulder, CO 80303. ^Some elements at Boulder, CO.
NisT Special Publication 800 21 Guideline foF Implementing

Cryptography in the

Federal Government

Annabelle Lee

COMPUTER SECURITY

Security Technology Group

Computer Security Division

National Institute of Standards

and Technology

Gaithersburg. MD 20899-cS930

November 1999

U.S. Department of Commerce

William M. Daley, Secretary

Technology Administration

Dr. Cheryl L. Shavers, Under Secretary of Commerce for Technology

National Institute of Standards and Technology

Raymond G. Kammer, Director
Reports on Computer Systems Technology

Tlic Information Technology Laboratory (ITL) at the National Institute of Standards and Technology (NIST)

promotes the U.S. economy and public welfare by providing technical leadership for the Nation's measurement and

standards infrastructure for information technology. ITL develops tests, test methods, reference data, proof of concept

implementations and technical analyses to advance the development and productive use of information technology. ITL's responsibilities include the development of technical, physical, administrative, and management standards and

guidelines for the cost-effective security and privacy of sensitive unclassified information in federal computer systems.

This Special Publication 800 series reports on ITL's research, guidance, and outreach efforts in computer security, and

its collaborative activities with industry, government, and academic organizations.

National Institute of Standards and Technology Special Publication 800-21

Natl. Inst. Stand. Technol. Spec. Publ. 800-21, 138 pages (Nov. 1999)

CODEN: NSPUE2

U.S. GOVERNMENT PRINTING OFFICE

WASHINGTON: 1999

For sale by the Supei intcndent of Documents, U.S. Government Printing Office, Washington, DC 20402-9325
GUIDELINE FOR IMPLEMENTING

CRYPTOGRAPHY IN THE FEDERAL GOVERNMENT

1. INTRODUCTION 1 1.1. Purpose 1 1.2. Audience 1 1.3. Scope 2

1.4. Content 3

1 .5. Uses of Cryptography 4

2. STANDARDS AND CRITERIA 6

2.1. Benefits of Standards 7

2.2. Standards Organizations 8

2.2.1 . American National Standards Institute (ANSI) 8

2.3.2. Institute of Electrical and Electronics Engineers (IEEE) 1

1

2.2.2. Internet Engineering Task Force (IETF) 1

1

2.2.3. International Organization for Standardization (ISO) ..12

2.3. Common Criteria 12

2.4. FIRS Waiver Procedure 13

3. SOME IMPLEMENTATION ISSUES 14

3. 1 . Interfaces/Use of CAPIs 14

3.2. Hardware vs. Software Solutions 14

3.2.1. Public vs. Secret Key Cryptography 15

3.3. Key Management 1

5

3.3.1. Key Generation 17

3.3.2. Key Use 18

3.3.3. Key Archiving 19

3.3.4. Key Destruction 20

3.4. Authentication 20

3.4. 1 . Traditional (Weak) Authentication 20

3.4.2. Authentication Using Dynamic Authentication Data 21

3.4.3. Authentication Against Active Attacks 22

4. CRYPTOGRAPHY METHODS 23

4.1 . Symmetric/Secret Key Cryptography 23

4.1 .1 . Symmetric/Secret Encryption 23

4. 1 .2. Message Authentication Code 27

4.2. Hash Functions 28

4.2.1. SHAandSHA-1 28

4.3. Asymmetric Key Cryptography 29

4.3.1. Digital Signatures 29

4.3.2. Key Transport/Agreement 37

4.4. Key Management ......42 5. PUBLIC KEY INFRASTRUCTURE (PKI) 44

5.1 . Public Key Infrastructure (PKI) Overview 44

5.2. PKI Architectures 45

5.3. Security Policies of Other CAs and the Network 46

iii
5.4. Interoperability 46

5.5. Minimum Interoperability Specification for PKI Components (MISPC)....47

5.6. Federal PKI Architecture 48

5.6.1 . Architecture Components 49

5.6.2. Operational Concept 51

5.6.3. Federal PKI (FPKI) Steering Committee 52

6. TESTING 53

6.1 . Cryptographic Module Validation Program (CMVP) 55

6.1.1. Background 55

6.1.2. FIPS PUB 140-1 Requirements 58

6.1.3. Validated Modules List 60

6.1.4. Effective Use of FIPS PUB 140-1 60

6.2. National Voluntary Laboratory Accreditation Program (NVLAP) 60

6.3. Industry and Standards Organizations. 60

6.3.1. National Information Assurance Partnership (NIAP) 61

6.4. Certification and Management Authorization 61

7. SELECTING CRYPTOGRAPHY - THE PROCESS 63

7.1. Planning Phase 67

7.1.1. Security Policies. 67

7.1.2. Risk Assessment 71

7.1.3. Security Objectives 73

7.2. Definition Phase. 74

7.2.1 . Security Requirements/Specifications 75

: 7.2.2. Cryptographic Method Example 83

7.2.3, Selecting Cryptographic Countermeasures 84

7.3. Acquisition Phase 94

7.3.1. Implementation Approach 95

7.4. Operations Phase 97

7.4.1. Training and Documentation 97

7.4.2. Life Cycle Management of Cryptographic Components 97

8. PUTTING IT ALL TOGETHER - EXAMPLES 99

8.1. Key Recovery Demonstration Project (KRDP) 99

8.1.1. Department of Energy: EZ_ERA32 and the KRDP 99

8.1.2. U.S. Electronic Grants 103

8.2. Army Corps of Engineers 106

8.2.1. ESS Architecture 107

8.2.2. Key Management 108

8.2.3. Signature Generation and Verification 109

8.3. Treasury Electronic Certification System 1 09

8.3.1. Program History 109

8.3.2. ECS Process ....110

8.3.3. Future Plans: Windows-Based ECS (WECS) 1 1

1

9. WHAT'S NEXT? 112

9.1 . Advanced Encryption Standard (AES) 112

9.1 .1 . Minimum Acceptability Requirements 112

9.1 .2. Evaluation Criteria 112

iv
9.1.3. AES Finalists 113

9.2. Key Agreement or Exchange 113

9.3. Key Recovery 113

9.4. Technical Advisory Committee 114

9.5. FIPS 140-2 114

APPENDIX A: ACRONYMS 1 1

5

APPENDIX B: TERMS AND DEFINITIONS 119

APPENDIX C: REFERENCE LIST 129

V

Implementing Cryptography

CHAPTER 1

1. INTRODUCTION

1.1. Purpose

In today's world, both private and public sectors depend upon information

technology systems to perform essential and mission-critical functions. In the

current environment of increasingly open and interconnected systems and

networks, network and data security are essential for the optimum use of this

information technology. For example, systems that carry out electronic financial

transactions and electronic commerce must protect against unauthorized access

to confidential records and unauthorized modification of data.

Cryptography should be considered for data that is sensitive, has a high value, or represents a high value if it is vulnerable to unauthorized disclosure or undetected modification during transmission or while in storage. Cryptographic

methods provide important functionality to protect against intentional and

accidental compromise and alteration of data. These methods support

communications security by encrypting the communication prior to transmission

and decrypting it at receipt. These methods also provide file/data security by

encrypting the data prior to placement on a storage medium and decrypting it after retrieval from the storage medium.

The purpose of this document is to provide guidance to Federal agencies on how

to select cryptographic controls for protecting Sensitive Unclassified^ information.

This document focuses on Federal standards documented in Federal Information

Processing Standards Publications (FIPS PUBs) and the cryptographic modules

and algorithms that are validated against these standards. However, to provide

additional information, other standards organizations, (e.g., American National

Standards Institute (ANSI) and International Organization for Standardization

(ISO)) are briefly discussed.

1.2. Audience

This document is intended for Federal employees, who are responsible for

designing systems, and procuring, installing, and operating security products to

meet identified security requirements. This document may be used by:

^ Hereafter referred to as sensitive information. In the Computer Security Act of

1987, Congress assigned responsibility to the National Institute of Standards and

Technology (NIST) for the preparation of standards and guidelines for the

security of sensitive Fee/era/ systems. Excluded are classified and sensitive

national security-related systems.

1
Implementing Cryptography

• A manager responsible for evaluating an existing system and determining

whether cryptographic methods are necessary,

• A technical specialist requested to select one or more cryptographic

methods/techniques to meet a specified requirement, or

• A procurement specialist developing a solicitation for a system or network

that will require cryptographic methods to perform security functionality.

The goal is to provide these individuals with sufficient information to allow them

to make informed decisions about the cryptographic methods that will meet their

specific needs to protect the confidentiality, authentication, and integrity of data

that is transmitted and/or stored in a system or network.

This document is not intended to provide information on the Federal

procurement process or provide a technical discussion on the mathematics of

cryptography and cryptographic algorithms.

1.3. Scope

This document limits its discussion of cryptographic methods to those that meet

Federal standards. (The majority of the information in this guideline may be

useful to both Federal and commercial personnel and applicable to all computer

networks and environments.) Both the Federal government and industry use

products that meet Federal standards and standards bodies such as ANSI have

also adopted Federal standards.

This guideline provides information on selecting cryptographic services and

methods and implementing the methods in new or existing systems. Specifically,

the guideline includes discussions of the following:

• The cryptographic products selection process. This may include one or more of the following:

; 1 . Performing a risk assessment (or other process) to identify the:

• assets that must be protected,

• vulnerabilities of the system, and

• threats that might exploit the vulnerabilities.

2. Identifying the security regulations and policies that are applicable to the system.

3. Specifying the cryptographic security requirements.

4. Specifying the security services that will address the needs identified in items 1 through 3 above.

2
Implementing Cryptography

• Implementation issues, including:

• implementation approach,

• life cycle management of cryptographic components,

• training for users, operators, and system engineers,

• key management,

• authentication techniques, and

• testing - certification, independent verification and validation (IV&V).

1.4. Content

The guideline is divided into three parts. Part one provides an overview of

selecting cryptographic services and products:

- Chapter 1 includes background information (purpose, audience, and

scope) and advantages of using cryptography.

- Chapter 2 defines the role and use of standards, describes standards

organizations that are outside the Federal government, and discusses the

new international security standard, the Common Criteria.

- Chapter 3 describes some implementation issues (e.g., key management,

authentication, and recommendations).

Part two focuses on specific methods:

- Chapter 4 describes the methods that are available for symmetric and

asymmetric key cryptography.

- Chapter 5 discusses the Public Key Infrastructure (PKI).

- Chapter 6 discusses testing, including the Cryptographic Module

Validation Program (CMVP).

Part three ties all of the information together:

- Chapter 7 describes the process of choosing types of cryptography and

selecting a cryptographic method or methods to fulfill a specific

requirement.

3
Implementing Cryptography

- Chapter 8 includes some examples of Federal projects that use

cryptography.

- Chapter 9 describes future activities.

There are three appendixes to the guideline:

- Appendix A includes an acronym list.

- Appendix B includes terms and definitions.

Appendix C includes a bibliography of cryptographic standards and

guidelines and cryptography texts.

A number of examples are included throughout this guideline. Each example is displayed in a shaded box for ease of viewing.

1.5. Uses of Cryptography

Cryptography is a branch of mathematics based on the transformation of data.

Cryptography deals with the transformation of ordinary text (plaintext) into coded

form (ciphertext) by encryption and the transformation of ciphertext into plaintext

by decryption. Cryptography relies upon two basic components: an algorithm (or

cryptographic methodology) and a key. The algorithm is the mathematical

function used for encryption or decryption, and the key is the parameter used in the transformation. These transformations are illustrated in Figure 1.

P— encryption

plaintext - P

_^ Q ciphertext - C

keys - K2

K2

decryption

(Note: Ki and K2 may be the same key or different keys)

Figure 1 . Data Transformation

There are two basic types of cryptography: secref /cey systems (also called

symmetric systems) and public A'ey systems (also called asymmetric systems).

In secret key systems, the same key is used for both encryption and decryption.

That is, all parties participating in the communication share a single key. In public key systems, there are two keys: a public key and a private key. The

public key used for encryption is different from the private key used for

4
Implementing Cryptography

decryption. The two keys are mathematically related, but the private key cannot

be determined from the public key.

In general, cryptography is used to meet the following security objectives:

• Confidentiality services restrict access to the content of sensitive data to

only those individuals who are authorized to view the data. Confidentiality

measures prevent the tvA7aty?/?or/zed disclosure of information to

unauthorized individuals or processes.

• Data integrity services address the unauthorized or accidental modification

of data. This includes data insertion, deletion, and modification. To

ensure data integrity, a system must be able to detect unautiiorized 6a\a

modification. The goal is for the receiver of the data to verify that the data

has not been altered.

• Auttientication services establish the validity of a transmission, message,

or an originator. (Authentication services also verify an individual's

authorization to receive specific categories of information. These services are not specific to cryptography.) Therefore, this service applies to both

individuals and the information itself. The goal is for the receiver of the

data to determine its origin.

• Non-repudiation services prevent an individual from denying that previous

actions had been performed. The goal is to ensure that the recipient of

the data is assured of the sender's identity.

5
Implementing Cryptography

CHAPTER 2

2. STANDARDS AND CRITERIA

Under the Information Technology Management Reform Act of 1 996 and the

Computer Security Act (CSA) of 1987 (Public Law 100-235), the National

Institute of Standards and Technology (NIST) is responsible for developing

technical standards and guidelines for Federal information resources. In addition, Appendix III to Office of Management and Budget (0MB) Circular No.

A-130 - Security of Federal Automated Information, in part, establishes a

minimum set of controls to be included in Federal automated information security

programs and assigns Federal agency responsibilities for the security of

automated information. The Appendix incorporates requirements of the

Computer Security Act of 1987.

Some of the standards and guidelines used to protect sensitive information are issued by NIST as FIPS PUBs. Federal agencies must comply with all mandatory standards and they are expected to:

- Support the development of such standards,

- Avoid the creation of different standards for government and the private

sector, and

- Use voluntary standards whenever possible,

Technically, NIST has authority to establish standards only for the Federal

government. However, FIPS PUBs have a profound effect on commerce and

industry. Since FIPS PUBs are established through a public process, the public

is aware of their existence, and industry often uses conformance to applicable

NIST standards as an evaluation factor when purchasing products. Also, NIST

has a long history of participation in industry standards groups, including ANSI,

ISO, Institute of Electrical and Electronics Engineers (IEEE), Internet Engineering

Task Force (IETF), and others. In some cases, the Federal government adopts

industry standards (ANSI X9.17 Key Management \Nas adopted with restrictions as FIPS PUB 171), and industry has adopted FIPS PUBs (e.g.. Data Encryption

Standard (DES) and DES Modes were adopted by ANSI).

Standards contain consistent technical specifications or other criteria to be used

as rules or guidelines to ensure that products, processes and services are

appropriate for their stated purpose.
Implementing Cryptography

2.1. Benefits of Standards

Standards are important because they define common practices, methods, and

measures/metrics. Therefore, standards increase the reliability and effectiveness

of products and ensure that the products are produced with a degree of quality.

Standards provide solutions that have been accepted by a wide community and

evaluated by experts in relevant areas. By using standards, organizations can

reduce costs and protect their investments in technology.

Standards provide for Information Technology (IT) interoperability, security, and

integrity:

• Interoperability. Products developed to a specific standard may be used

to provide interoperability with other products that conform to the same

standard. By using the same cryptographic algorithm, data that was

encrypted using vendor A's product may be decrypted using vendor B's

product. The use of a common standards-based cryptographic algorithm

is necessary, but may not be sufficient to ensure product interoperability.

Other common standards, such as communications protocol standards,

may also be necessary.

By ensuring interoperability among different vendors' equipment,

standards permit an organization to select from various available products

to find the most cost-effective solution.

• Security. Standards may be used to establish a common approved level

of security. Most agency managers are not cryptographic security

experts, and, by using a FIPS approved cryptographic algorithm, a

manager knows that a standard has been developed and the algorithm

has been tested against this standard and the results validated by NIST.

NIST validation means the algorithm has been found to be adequate for

the protection of sensitive government data. In addition, most FIPS

approved algorithms have gone through a significant period of public

analysis and comment.

• Integrity. Standards may be used to assure the integrity of a product.

Standards may:

• Specify how a feature is to be implemented, e.g., the feature must be

implemented in hardware.

• Require a test or alarm to detect a malfunction.

• Require specific documentation to assure proper implementation and

product change management.

7
Implementing Cryptography

Many FIPS PUBs contain associated conformance tests and specify the

conformance requirements. The conformance tests may be administered

by NIST accredited laboratories and provide validation that the standard

was correctly implemented in the product.

• Common Form of Reference. A standard may become a common form

of reference to be used in evaluating vendors' products. FIPS PUB 140-1

,

Security Requirements for Cryptographic Modules, contains security and

integrity requirements for any cryptographic module implementing

cryptographic operations. FIPS PUB 140-1 establishes a common form of

reference by defining four levels of security for each of eleven security

attributes.

• Cost Savings. A standard can save a great deal of money by providing a

single commonly accepted specification. Without standards, users may

be required to become experts in every IT product that is being considered

for purchase. Also, without standards, products may not interoperate with

products purchased by other users. This will result in a significant waste

of money or in the delay of implementing IT.

2.2. Standards Organizations

NIST develops standards that are used by vendors who are developing security

products, components, and modules. These products may be purchased and

used by Federal government agencies. In addition, there are other groups that

develop and promulgate standards. The following organizations are briefly

described below: ANSI, IEEE, IETF, and ISO.

2.2.1 . American National Standards Institute (ANSI) ^

The American National Standards Institute (ANSI) is the administrator and

coordinator of the United States (U. S.) private sector voluntary standardization

system. ANSI is a private, nonprofit membership organization supported by a

diverse constituency of private and public sector organizations. ANSI does not

itself develop American National Standards; rather it facilitates development by

establishing consensus among qualified groups.

The primary goal of ANSI is the enhancement and global competitiveness of U.S.

business. ANSI promotes the use of U.S. standards internationally, advocates

U.S. policy and technical positions in international and regional standards

^ The information in this section was taken from the ANSI web site:

www.ansi.orq .

8
Implementing Cryptography

organizations, and encourages the adoption of international standards as

national standards where these meet the needs of the user community.

2.2.1.1. ANSIX9

X9 is an inter-industry user and developer of technical standards and is organized into sub-committees and working groups, as illustrated in Figure 2.

X9F

Information Security

Standards

X9F1

Cryptographic

Tools

X9F2

Security

Guidelines

X9F3

Cryptographic

Protocols

X9F4

Applications

Figure 2. ANSI X9F Organization

The Accredited Standards Committee - X9 (banking) and F (security) Financial

Services manages the development of information security and other standards

for the financial services industry. The following ANSI standards are designed to

support financial information infrastructures:

- Hash and signature algorithms

- Certificate management standards

- Key management and key agreement standards

- Other cryptographic methods

Table 1 lists FIPS PUBs and the corresponding ANSI standards. Some of the

proposed ANSI standards may be considered for reference in existing FIPS

PUBs after they have been adopted by ANSI.

Table 1. FIPS PUBs and Corresponding ANSI Standards

FIPS PUB ANSI STANDARD

Symmetric Encryption

DES - FIPS PUB 46-3,

government tests

ANSI X3.92 - Data Encryption

Algoritlim

DES - FIPS PUB 46-3 and

ANSI tests

ANSI X9.52 - Triple Data Encryption

Algorithm, AHS\TG-^ 9 tests (also

published as NIST Special Publication

(SP) 800-20)

Advanced Encryption

Standard (AES) (TBD FIPS PUB

and TBD government tests)

(eventual proposal to ANSI)

9
Implementing Cryptography

Table 1. FIPS PUBs and Corresponding ANSI Standards

(Concluded)

1 FIPS PUB ANSI STANDARD

Digital Signature Standard

(DSS) - FIPS PUB 186-2,

nn\/prnrnpnt tp^t^

ANSI X9.30 - Part 1 : The Digital

Signature Algorithm (DSA)

DinitPil Sinnritiirp St^ndrirH

(DSS) -FIPS PUB 186-2

ANSI X9 31 - rDSA Sianature^

Algorithm, draft tests

Dinital L/iyilCll OI^IICllUIC Qinnatiiro OlClllUCllvJ QtanrlarH

(DSS) - FIPS PUB 186-2

AM9I XQ RP - Fllinfir Cliinm Dinital

Signature Algorithm (ECDSA), draft

tests

Data Ai itht^ntir^PitirMi Data Authentication Code (DAC)

- FIPS PUB 113

ANSI X9.9 - American National

Standard for Financial Institution

Message Authentication^

r\uy MailbUUiUlvlailctycfilclil

Key Management Using ANSI

X9.17- FIPS PUB 171

ANSI X9.17 - Financial Institution Key

Management

ropose auoption lor

UUVUi 1 H 1 lUl 1 L UoU dllUI dUUpioU do

approved ANSI standard)

rtraft AMQI YQ AO Anraamant nf

\Dyi 1 II 1 Icii lly fxtyyo KJoll ly Lyi^UlGlU

Logarithm Cryptography, TBD tests

.

ropObc aUUpilUri lOI government use after adopted as

dppiUVt?U MInOI oldllUdiU^

Uldll MInOI A57.H*+ — / lie 1 lailopUil Ui

Symmetric Algorithm Keys Using

nuvuisiuiG lUuiiiy r\uy y^iypiuyiapi ly,

TBD tests

^Prnnn^p aHnntinn for

government use after adopted as approved ANSI standard)

draft ANSI X9 63 - Kev Aareement

and Key Transport Using Elliptic

Curve-based Cryptography, TBD tests

Hash Function

Secure Hash Standard (SHSj

- FIPS PUB 180-1

ANSI X9.30 - 1 993 Part 2: The

Secure Hash Algorithm (SHA-1)

Cryptographic Moduie Validation

Program

FIPS PUB 140-1, government

tests

draft ANSI X9.66 - Cryptography

Device Security

^ This standard was withdrawn by ANSI in 1999.

This standard was withdrawn by ANSI in 1999.

10
Implementing Cryptography

2.3.2. Institute of Electrical and Electronics Engineers (lEEE)^

The technical objectives of the IEEE focus on advancing the theory and practice

of electrical, electronics and computer engineering, and computer science. The

goals of IEEE activities are to: (1) enhance the quality of life for all peoples

through improved public awareness of the influence and applications of its technologies and (2) advance the standing of the engineering profession and its members.

IEEE develops and disseminates voluntary, consensus-based industry standards

involving leading-edge electro-technology. IEEE supports international

standardization and encourages the development of globally acceptable

standards.

2.2.2. Internet Engineering Task Force (lETF)^

The IETF is a large open international community of network designers,

operators, vendors, and researchers concerned with the evolution of the Internet

architecture and the smooth operation of the Internet. The actual technical work

of the IETF is done in working groups, which are organized by topic into several areas (e.g., routing, transport, security, etc.). The primary role of the Security

Area Directorate and the Security Area Advisory Group is to provide help to IETF

working groups on how to provide for security in the protocols they design.

2.2.2.1 . IETF Public-Key Infrastructure (X.509) (pkix) Working Group

Many Internet protocols and applications which use the Internet employ publickey technology for security purposes and require a public-key infrastructure (PKI)

to securely manage public keys for widely-distributed users or systems. The

X.509 standard constitutes a widely-accepted basis for such an infrastructure,

defining data formats and procedures related to distribution of public keys via

certificates digitally signed by certification authorities (CAs).

The task of the pkix working group will be to develop Internet standards needed

to support an X.509-based PKI. The goal of this PKI will be to facilitate the use

of X.509 certificates in multiple applications that make use of the Internet and to

promote interoperability between different implementations choosing to make use

of X.509 certificates. The resulting PKI is intended to provide a framework that

will support a range of trust/hierarchy environments and a range of usage

environments. The group will focus on tailoring and profiling the features

^ The information in this section was taken from the IEEE web site:

www.ieee.orq. ^ The information in this section was taken from the IETF web site: ietf.orq .

11
Implementing Cryptography

available in the v3 X.509 certificate to best match the requirements and

characteristics of the Internet environment.

2.2.3. International Organization for Standardization (ISO)^

ISO is a worldwide federation of national standards bodies from 100 countries.

ISO is a non-governmental organization. Its mission is to promote the

development of standardization and related activities in the world with a view to

facilitating the international exchange of goods and services, and to developing

cooperation in the spheres of intellectual, scientific, technological and economic

activity. ISO's work results in international agreements that are published as

International Standards.

The technical work of ISO is carried out in technical committees, subcommittees

and working groups. In these committees, qualified representatives of industry,

research institutes, government authorities, consumer bodies, and international

organizations from all over the world come together in the resolution of global

standardization problems.

2.3. Common Criteria

The Common Criteria (CC) is referenced throughout this guidance document.

The CC represents the outcome of efforts to develop criteria for evaluation of IT

security. These criteria will be used throughout the international community. The

CC defines a set of IT requirements of known validity that can be used in establishing security requirements for prospective products and systems. The

CC also defines the Protection Profile (PP) construct that allows prospective

consumers or developers to create standardized sets of security requirements

that will meet their needs. The CC presents requirements for the IT security of a

product under the distinct categories of functional requirements and assurance

requirements.®

The CC is a uo/t/n fa Ay standard used to describe the security properties

(functional and assurance) of IT products (or classes of products) and systems.

In essence, the CC is a standard security specification "language." Products

whose security properties have been specified using the CC may then be

validated (tested) for conformance to their CC specifications. Such a validation,

when performed by an accredited testing laboratory, confirms that the product

meets its security specification(s).

In general, the FIPS PUBs referenced in this Guideline are mandafo/y standards

that must be met. For example, FIPS PUB 46-3, Data Encryption Standard, is a

The information in this section was taken from the ISO web site: www.iso.ch . ^ This information was extracted from documents located at: csrc.nist.qov/cc/info/cc-summ .

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Implementing Cryptography

specific set of technical security requirements for the Data Encryption Standard

algorithm.

When developing a specification or criteria for selection a cryptographic

module/product, both the CC and FIPS PUBs may be used. The CC may be

used to specify the functions the algorithm will perform. The FIPS PUBs

designate the specific type of algorithm (DES, DSA) and the level of independent

testing required (FIPS PUB 140-1).

2.4. FIPS Waiver Procedure

Under certain exceptional circumstances, the heads of Federal agencies may

approve waivers to FIPS. Waivers should be granted only when:

a. Compliance with a standard would adversely affect the

accomplishment of the mission of an operator of a Federal computer

system, or

b. Cause a major adverse financial impact on the operator that is not

offset by Government-wide savings.

Agency heads may approve waivers only by a written decision that explains the

basis on which the agency head made the required finding(s).

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Implementing Cryptography

CHAPTER 3

3. SOME IMPLEMENTATION ISSUES

There are many issues that are applicable to the implementation of security

methods/products. These are extensively discussed in other documents such as

The NIST Handbook (SP 800-1 2), Generally Accepted Principles and Practices

for Security Information Technology Systems (SP 800-14) and 0MB Circular A1 30, Security of Federal Automated Information Resources, Appendix III. Of

particular relevance are the sections on training, contingency planning,

assignment of roles and responsibilities, and security violation reporting and

response. This chapter focuses on implementation issues that are specific to

cryptography.

3.1 . Interfaces/Use of CAPIs^

As application developers become aware of the need for cryptographic

protection, they are adding "hooks" to access the cryptographic functionality

developed by others. These "hooks" are known as the CAPI, or cryptographic

application programming interface. A CAPI is an interface to a library of

functions that software developers can call upon for security and cryptography

services. Applications that utilize a standard CAPI can access multiple

cryptographic implementations through a single interface. For example, a CAPI

for confidentiality could interface with different products and algorithms without

affecting the basic application. The goal of a CAPI is to make it easy for

developers to integrate cryptography into applications. CAPIs can be targeted at

different levels of abstraction, ranging from cryptographic module interfaces to

authentication service interfaces. The goal is for general-purpose applications

(e.g., spreadsheets, document processors, e-mail) to be cryptographically

unaware, utilizing only a minimum number of high-level security calls without

having to know about the underlying cryptography and security support (e.g.,

certificate management, key management, data isolation). Ideally, these calls

would require no knowledge of specific cryptographic algorithms or modules.

3.2. Hardware vs. Software Solutions

The trade-offs among security, cost, simplicity, efficiency, and ease of

implementation need to be evaluated. Cryptography can be implemented in hardware, software and/or firmware - each has its related costs and benefits.

Historically, software has been less expensive and slower than hardware,

although for large applications, hardware may be less expensive. In addition,

software is easier to modify or bypass than equivalent hardware products. The

^ The information in this section was extracted from the NBA Report, Security

Service API: Cryptographic API Recommendation Second Edition.

14
Implementing Cryptography

advantages of software solutions are in flexibility and portability, ease of use, and

ease of upgrade.

In many cases, cryptography is implemented in a hardware device but is controlled by software and, therefore, a hybrid solution is provided. Again, the user must evaluate the solutions against requirements to determine the best

solution.

3.2.1. Public vs. Secret Key Cryptography

The primary advantage of public-key cryptography is increased security and

convenience: private keys never need to transmitted or revealed to anyone. In a

secret-key system, the secret keys must be transmitted (either manually or through a communication channel). There may be a chance that an

unauthorized individual can access the secret keys during their transmission.

The primary advantage of secret key cryptography is speed. There are popular

secret-key encryption methods that are significantly faster than any currently

available public-key encryption method. Alternatively, public-key cryptography

can be used with secret-key cryptography to get the best of both worlds: the

security advantages of public-key systems and the speed advantages of secretkey systems. The public-key system can be used to encrypt a secret key that is used to encrypt the bulk of a file or message.

In some situations, public-key cryptography is not necessary and secret-key

cryptography alone is sufficient. This includes environments where secure

secret-key agreement can take place; environments where a single authority

knows and manages all the keys; and a single-user environment. In general,

public-key cryptography is best suited for an open multi-user environment.

3.3. Key Management

The proper management of cryptographic keys is essential to the effective use of

cryptography for security. Ultimately, the security of information protected by

cryptography directly depends on the protection afforded the keys. All keys need

to be protected against modification, and secret and private keys need to be

protected against unauthorized disclosure. Listed below are recommendations

for effective key management.

- Make sure that users are aware of their liabilities and responsibilities, and that

they understand the importance of keeping their keys secure.

The security of cryptographic keys in an electronic or digital signature system is the foundation of a secure system; therefore, users must maintain control of their

keys! Users must be provided with a list of responsibilities and liabilities, and

each user should sign a statement acknowledging these concerns before

15
Implementing Cryptography

receiving a key (if it is a long-term, user-controlled key). If different user roles

(e.g., security officer, regular user) are implemented in a system, users should be

aware of their unique responsibilities, especially regarding the significance of a

key compromise or loss.

- Prepare for the possibility of compromise

It is imperative to have a plan for handling the compromise or suspected

compromise of central/root keys or key components at a central site; this should

be established before the system goes "live." The contingency plan should

address what actions should be taken with system software and hardware,

central/root keys, user keys, previously generated signatures, encrypted data,

etc.

If someone's private key is lost or compromised, others must be made aware of

this, so that they will no longer encrypt messages using the invalid public key nor accept messages signed with the invalid private key. Users must be able to

store their private keys securely, so that no intruder can find them, yet the keys

must be readily accessible for legitimate use. Keys need to be valid only until a

specified expiration date.

- Sign and verify tine code that implements the cryptographic functions.

Software at the central key management site should be electronically signed and

periodically verified to check the integrity of the code. This provides a means of

detecting the unauthorized modification of system software. Within a

cryptomodule, this feature of generating and verifying a cryptographic checksum

is required by FIPS PUB 140-1.

- A system implemented for a Federal government agency should have its centrally stored keys and system software controlled by Federal employees.

Proper control of central/root keys and key management software and hardware

is critical to the security of the system. In the situation where a Federal agency

operates a system that was developed by a contractor, Federal employees

should be in control of this material. This also applies to configuring the key

management hardware and software. Once the system goes live, unlimited

access to central data, code, and cryptomodules should not be given to nonFederal employees, including those who were contracted to develop and/or

maintain the system.

- Secure Key Management

Key management provides the foundation for the secure generation, storage,

distribution, and translation of keys. One of the fundamental principles for

16
Implementing Cryptography

protecting keys is the practice of split knowledge^° and dual controPV Split

knowledge and dual control may be used to protect the centrally stored user

secret keys and root private keys, secure the distribution of user tokens, and

initialize all cryptomodules in the system to authorize \he\r use in performing

cryptographic functions within a system. Another role of key management is key

maintenance, specifically, the update/replacement of keys at the completion of a

cryptoperiod. The cryptoperiod is determined based on the sensitivity of the

information and the risk of key compromise.

Central sites play an important role in key management. In public-key systems,

central sites typically include a CA, which is an entity that issues and revokes

public key certificates and may even generate key pairs. The CA private key

should be protected with split knowledge and dual control. Whether in a secret- or public-key system, the security of the central site is critical to the overall

cryptographic security of the system.

3.3.1. Key Generation

The generation of keys is the most sensitive of all cryptographic functions. Any

inadequacies in the implementation of the key generation function or in the

physical security safeguards of that function will seriously undermine the integrity

of other cryptographic mechanisms. The physical security measures are necessary to prevent unauthorized disclosure, insertion, and deletion of the

system or keys produced by the system. Specifically, all automated resources which generate keys and initialization vectors (IVs) should be physically

protected to prevent the:

- disclosure, modification, and replacement of the keys,

- modification or replacement of the IVs,

- modification or replacement of the generation algorithm, or device.

Depending on the desired management structure, there are some applications

where the generation of keys is desirable and other applications where the

distribution of keys from another source, such as a central authority, may be

more desirable.

- Maintaining control of central or root keys from the time of generation is

critical.

A condition under which two or more parties separately possess key

components, which, individually, convey no knowledge of the resultant

cryptographic key. The resultant key exists only within secure equipment.

A process of utilizing two or more separate entities (usually persons) operating

in concert, to protect sensitive functions or information.

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Implementing Cryptography

Central or root keys are most likely to be used in sensitive applications such as

encrypting user keys, signing a central key database for integrity, binding a key

pair to a user, or generating user keys. If these keys are compromised, a

complete system compromise (involving the compromise of user keys, encrypted

data, and/or signed data) becomes a very real threat. It is essential to maintain

the security of these central keys from the very beginning - the generation

process. No one but the proper owner(s) of a key or key component should ever be able to use that key or key component. If split knowledge and dual control are a requirement for central or root keys, then a failure to maintain split knowledge

and dual control of those keys at any time in their lifecycle could present both a

security problem and a potential system compromise.

- If a key is stored on a token, and a PIN is used to access the token, then only

that token's owner should ever have possession of both the token and its corresponding PIN.

This applies to root security officers who may generate a token and its Personal

Identification Number (PIN), as well as any intermediaries. To prevent a courier

from having sole control of both items, security officers should distribute the

token and PIN in separate mailings (in separate packages mailed on different

days). Also, different roles should be used to generate and mail PINs. Receipt

of each item should always be confirmed to the original sender. A failure to

maintain control of a token and its corresponding PIN could lead to a key

compromise and the misuse of cryptographic functions within the system.

3.3.2. Key Use

- Cryptographic keys may need special physical protection.

If keys or key components are stored on a token (e.g., floppy disk, personal

computer (PC) Card, smartcard, etc.), this token may have to be stored in a

special manner to prevent unauthorized individuals from accessing the key or key component. For example, if key components for starting a CA or Key

Management Facility are stored on tokens which are secured in a safe, multiple

people might have access to this token. Therefore, additional protection is needed for each token, possibly by using a tamper-evident envelope, to enable

the token's owner to determine if another person used a token.

- Authentication timeout features are important for protecting keys from

compromise or misuse.

An authentication timeout feature for a cryptographic module or token is important to minimize the possibility of an unauthorized individual accessing an

"active" cryptomodule and using its cryptographic keys. This could happen if a

cryptomodule is left unattended by a user who has authenticated to it and loaded

his/her cryptographic keys. One alternative is to force a user to periodically

18
Implementing Cryptography

reauthenticate oneself to a cryptomodule, rather than allow him/her to stay

logged in for an indefinite amount of time. For sensitive applications, it may be

necessary to restrict the hours during which this can take place.

- Sign all centrally stored data and encrypt sensitive data, such as secret keys

that are used to provide confidentiality.

All centrally stored data that is related to user keys should be signed for integrity,

and possibly encrypted for confidentiality (all user secret keys and CA private

keys should be encrypted). Individual key records in a database - as well as the

entire database - should be signed. To enable tamper detection, each individual

key record should be signed, so that its integrity can be checked before allowing

that key to be used in a cryptographic function. When signing the entire

database, at least the important fields that do not change regularly should be

signed (this allows for faster verification).

- Provide for key recovery capabilities.

IT systems must protect the confidentiality of information. There must be

safeguards to ensure that sensitive records are neither irretrievably lost by the

rightful owners nor accessed by unauthorized individuals. Key recovery

capabilities provide these controls. All key components should be available to an

organization regardless of whether the associated user is currently working in the

organization. Employees leave organizations voluntarily and some are removed

and in either situation, the organization may need to access the key components

to recover encrypted data. Key recovery capabilities allow organizations to

restore key components.

It is very important to have backup copies of central/root keys, since the

compromise or loss of those components could prevent access to keys in the

central database, and possibly deny system users the ability to decrypt data or perform signature verifications.

3.3.3. Key Archiving

- Archive user keys for a sufficiently long cryptoperiod.

A cryptoperiod is the time during which a key can be used for signature

verification or decryption; it should extend well beyond the lifetime of a key

(where the lifetime is the time during which a key can be used to generate a

signature and/or perform encryption). Keys should be archived for a lengthy

cryptoperiod (on the order of decades), so that they can be used to verify

signatures and decrypt ciphertext during the cryptoperiod.

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3.3.4. Key Destruction

- Determine reasonable lifetimes for keys associated with different types of

users.

Users with different roles in the system should have keys with lifetimes that take

into account the users' roles and responsibilities, the applications for which the

keys are used, and the security services which are provided by the keys

(user/data authentication, confidentiality, data integrity, etc.). Reissuing keys

should not be done so often that it becomes burdensome; however, it should be

performed often enough to minimize the loss caused by a possible key

compromise.

- Handle the deactivation/revocation of keys so that data signed prior to a

compromise date (or date of loss) can be verified.

It should be possible to designate a signing key as "lost" or "compromised," so

signatures generated prior to a specified date can be verified. Otherwise, all data

previously signed with a lost/compromised key would have to be reviewed and

re-signed.

3.4. Authentication^^

One of the primary security controls to ensuring individual accountability

(determining the identity of the user) is to authenticate each user. Traditional

authentication techniques include passwords and PINs. Additional methods for

authenticating users are provided by cryptographic methods. The following

discussion compares traditional and cryptographic techniques. The discussion

makes the assumption that both the claimant's and verifier's local environments

are trusted. The protections described are aimed at the communications path

between a claimant (user) and a verifier.

3.4.1. Traditional (Weak) Authentication

Weak authentication only provides protection against attacks in which an

impostor cannot view, insert or alter the information passed between the user who is trying to prove identity (claimant) and the system checking on the

claimant's identity (verifier) during an authentication exchange and subsequent

sessions. In this scenario, an impostor attempts to assume a claimant's identity

by initiating an access control session as a valid user and attempting to guess a

legitimate user's authentication data.

Information in this section was based on an unpublished paper developed by J. Dray, NIST.

20
Implementing Cryptography

Traditional password schemes provide weak authentication because an impostor

may be able to view and later use the password to assume the user's identity.

The strength of this authentication process is highly dependent on the difficulty of

guessing password values and how well these values are protected.

3.4.2. Authentication Using Dynamic Authentication Data

This type of authentication mechanism relies on dynamic authentication data that

changes with each authenticated session between a claimant and verifier. An

impostor who can view information passed between a claimant and verifier may

attempt to record this information, initiate a separate access control session with

the verifier, and replay the recorded authentication data in an attempt to assume

the claimant's identity. This authentication mechanism protects against such

attacks, because authentication data recorded during a previous session will not

be valid for any subsequent sessions.

However, this type of authentication does not provide protection against active

attacks in which the impostor is able to alter the content or flow of information

between the claimant and verifier after a legitimate session has been

established. If the verifier binds the claimant's identity to the logical

communications channel for the duration of the session, the verifier believes that

the claimant is the source of all data received through this channel.

One-time passwords and Digital Signature Authentication (as described in FIPS

PUB 196) provide this level of protection.

3.4.2.1. Entity Authentication Using Public Key Cryptography

Authentication based on public key cryptography has an advantage over many

other authentication schemes because no secret information has to be shared by

the entities (parties A and B) involved in the exchange. Party A (claimant) uses a

private key to digitally sign a random number "challenge" issued by Party B

(verifier). If Party B can successfully verify the signed response using Party A's

public key, then Party A has been successfully authenticated.

FIPS PUB 196 specifies two challenge-response protocols by which entities in a

computer system may authenticate their identities to one another. In the

unilateral authentication protocol, one entity is the claimant and the other is the

verifier. In the mutual authentication protocol, each entity acts as both a claimant

and a verifier. These protocols may be used during session initiation, and at any

other time that entity authentication is necessary. Depending on which protocol

is implemented, either one or both entities involved may be authenticated. The

authentication protocols in this standard may be used in conjunction with other

public key-based systems (e.g., a public key infrastructure that uses public key

certificates) to enhance the security of a computer system.

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To acceptably implement this standard, an implementation must meet the

following criteria:

1) Each entity in an authentication exchange must use a FIPS approved

digital signature algorithm to generate and/or verify digital signatures;

2) Each entity must generate (pseudo)random numbers using a FIPS

approved (pseudo)random number generator;

3) Each entity acting as a claimant must be bound to a public/private key

pair; the private key should remain in the sole control of the claimant who

uses that key to sign a random challenge. The key binding requires a

unique authentication identifier for each claimant, so that a verifier can

distinguish between multiple claimants; and

4) One or both of the authentication protocols in FIPS PUB 196 must be

implemented. For each protocol, steps and token fields marked as

[OPTIONAL] do not need to be implemented, except where indicated

otherwise. However, all other steps and token fields must be

implemented.

3.4.3. Authentication Against Active Attacks

This type of authentication provides protections against impostors who can view,

alter, and insert information passed between a claimant and verifier even after

the claimant/verifier authentication is complete. These are typically referred to as

active attacks, since they assume that the impostor can actively influence the

connection between claimant and verifier. One way to provide this type of

authentication is to implement a digital signature algorithm to every bit of data

that is sent from the claimant to the verifier. There are other combinations of

cryptography that can provide this form of authentication, however, some type of

cryptography must be provided to every bit of data that is sent, othenwise any

unprotected bit will be suspect. Authentication against active attacks could

include encryption and digital signatures.

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CHAPTER 4

4. CRYPTOGRAPHY METHODS

The objective in this chapter is to provide a brief overview of the various

cryptographic methods that are available. The information is extracted from FIPS

PUBs and ANSI Standards. For more detailed information, reference the

complete standard or publication.

4.1. Symmetric/Secret Key Cryptography

In symmetric key cryptography, the sender and receiver of a message use a

shared secret key.

4.1.1. Symmetric/Secret Encryption

In symmetric/secret encryption, the sender uses a secret key to encrypt the

message and the receiver uses the same secret key to decrypt the message.

4.1 .1 .1 . Data Encryption Standard (DES)^^

The Data Encryption Standard (DES), initially issued in 1977, provides an

encryption algorithm for protecting Federal sensitive information from

unauthorized disclosure or undetected modification during transmission or while

in storage. DES was developed to protect sensitive computer data in Federal

computer systems against a number of passive and active attacks in communications and computer systems. Based on secret key cryptography, the

standard was initially issued for government use. DES is a publicly known cryptographic algorithm that converts plaintext to

ciphertext using a key that consists of 64 binary digits ("0"s or "1"s) of which 56

bits are randomly generated and used directly by the algorithm. The other 8 bits,

which are not used by the algorithm, are used for error detection. The DES

consists of 16 "rounds" of operations that mix the data and key together in a

prescribed manner using the fundamental operations of permutation and

substitution. The same algorithm is used with the same key to convert ciphertext

back to plaintext. Authorized users of encrypted computer data must have the

key that was used to encipher the data in order to decrypt it.

The unique key chosen for use in a particular application makes the results of

encrypting data using the algorithm unique. Selection of a different key causes

the cipher that is produced for any given set of inputs to be different. The

cryptographic security of the data depends on the security provided for the key

used to encipher and decipher the data.

The information in this section was extracted from FIPS PUB 46-3 (DES).

23
Implementing Cryptography

Data can be recovered from cipher only by using exactly the same key used to

encipher it. Unauthorized recipients of the cipher who know the algorithm but do

not have the correct key cannot derive the original data algorithmically.

However, anyone who does have the key and the algorithm can easily decipher

the cipher and obtain the original data.

Early versions of the DES required that the encryption algorithm be implemented

in electronic hardware and firmware. The DES standard allows for

implementation of the cryptographic algorithm in software, firmware, hardware, or any combination thereof to enable more flexible, cost-effective implementations.

FIPS PUB 81 , DES Modes of Operation, describes four different modes for using

the algorithm described in this standard. These four modes are called the:

- Electronic Codebook (ECB) mode. ECB is a direct application of the DES

algorithm to encrypt and decrypt data.

- Cipher Block Chaining (CBC) mode. CBC is an enhanced mode of ECB

which chains together blocks of cipher text;

- Cipher Feedback (CFB) mode. CFB uses previously generated cipher

text as input to the DES to generate pseudorandom outputs which are combined with the plaintext to produce cipher, thereby chaining together

the resulting cipher; and

- Output Feedback (OFB) mode. OFB is identical to CFB except that the

previous output of the DES is used as input in OFB while the previous

cipher is used as input in CFB. OFB does not chain the cipher.

The DES standard became effective July 1977. It was reaffirmed in 1983, 1988,

1993, and 1999.

Note: It is anticipated that triple DES and the Advanced Encryption Standard

(AES) will coexist as FIPS approved algorithms allowing for a gradual transition

to AES.

4.1.1.2. Triple DES (SDESy*

A more secure method for using the DES algorithm in three operations, called

Triple DES, has been developed by the private sector. The DES standard was

revised in 1999 to include Triple DES:

The information in this section was extracted from ANSI X9.52.

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Implementing Cryptography

1 . Triple DES (i.e., IDEA) as specified in ANSI X9.52 will be

recognized as a FIPS approved algorithm.

2. Triple DES will be the FIPS approved symmetric encryption

algorithm of choice.

3. Single DES (i.e., DES) will be permitted for legacy systems only.

New procurements to support legacy systems should, where

feasible, use Triple DES products running in the single DES

configuration.

4. Government organizations with legacy DES systems are encouraged to transition to Triple DES based on a prudent strategy

that matches the strength of the protective measures against the

associated risk.

The Triple Data Encryption Algorithm (TDEA) modes of operation are used for

both enciphering and deciphering operations. These modes are based on threefold compound operations of encryption and decryption using the Data

Encryption Algorithm (DEA). If two or three independent keys are used for three

DEA operations, it may extend the effective key space of DEA. Certain modes

also provide increased protection against more sophisticated attacks.

TDEA supports direct extension of the four DEA modes of operation, so that

backward compatibility with single DEA may be maintained. A TDEA mode of

operation is backward compatible with its single DEA counterpart if, with a proper

keying option for TDEA operation,

1 . An encrypted plaintext with single DEA mode of operation can be

decrypted correctly by the corresponding TDEA mode of operation; and

2. An encrypted plaintext with TDEA mode of operation can be decrypted

correctly by the corresponding single DEA mode of operation.

For throughput performance improvement in multiple processor systems,

interleaved and pipelined versions of these modes are specified. The modes of

operation are:

- TDEA Electronic Codebook Mode (TECB)

- TDEA Cipher Block Chaining Mode (TCBC)

- TDEA Cipher Block Chaining Mode - Interleaved (TCBC-I)

- TDEA Cipher Feedback Mode (TCFB)

- TDEA Cipher Feedback Mode - Pipelined (TCFB-P)

- TDEA Output Feedback Mode (TCFB)

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Implementing Cryptography

- TDEA Output Feedback Mode - Interleaved (TOFB-I)

The TECB, TCBC, TCFB and TOFB modes are based on the ECB, CBC, CFB

and OFB modes obtained by substituting DEA encryption/decryption operations

with TDEA encryption/decryption operations.

For applications in which high TDEA encryption/decryption throughput is important or in which propagation delay must be minimized, the new interleaved

(for TCBC and TOFB) and pipelined (for TCFB) modes are provided. In an

interleaved mode, the plaintext sequence is split into three subsequences of

plaintext. The encryption can be done simultaneously. In a pipelined mode, the

encryption is initiated with three IVs at three clock cycles so that after initiation,

the three DEA functional blocks can process the data simultaneously.

For all TDEA modes of operation, the three cryptographic keys (Ki, K2, K3) define a TDEA key bundle. The bundle and the individual keys must:

a. Be secret;

b. Have integrity;

c. Be used in the appropriate order as specified by the particular mode;

d. Be considered a fixed quantity in which an individual key cannot be

manipulated while leaving the other two keys unchanged; and

e. Cannot be unbundled for any purpose.

4.1.1.3. SKIPJACK^^

SKIPJACK is a symmetric encryption/decryption algorithm. SKIPJACK is a 64-bit

codebook using an 80-bit cryptovariable (session key). The session key is used

to encrypt plaintext information and to decrypt resulting ciphertext to obtain the

data. There are 32 rounds of processing per single encrypt/decrypt operation.

SKIPJACK can be used in any one of the four operating modes defined in FIPS

PUB 81 for use with DES:

Output Feedback (OFB),

Cipher Feedback Modes (CFB),

Electronic Codebook (ECB), and

Cipher-Block Chaining (CBC).

The SKIPJACK encryption/decryption algorithm has been approved for

government applications requiring encryption of sensitive but unclassified data

The information in this section was extracted from Skipjack and KEA Algorithm

Specifications, Version 2.0.

26
Implementing Cryptography

telecommunications. Data for purposes of this standard includes voice, facsimile

and computer information communicated in a telephone system.

4.1.1.4. Advanced Encryption Standard (AES)

In 1993, the following statement was included in the DES standard:

"At the next review (1998), the algorithm specified in this standard will be over

twenty years old. NIST will consider alternatives that offer a higher level of

security. One of these alternatives may be proposed as a replacement

standard at the 1 998 review."

NIST foresees that a multi-year transition period to the Advanced Encryption

Standard (AES) will be necessary to move toward any new encryption standard

and that DES will continue to be of sufficient strength for many applications.

(AES is discussed further in section 9.1 .)

4.1.2. Message Authentication Code^^

A data authentication algorithm (DAA) may be used to detect unauthorized

intentional and accidental data modifications. DES is the basis for the DAA. By

applying the DES algorithm, a Message Authentication Code (MAC) is calculated

on and appended to information. The MAC provides for integrity using a

cryptographic checksum value. To verify that the information has not been

modified at some later time, the MAC is recalculated on the information. The

new MAC is compared with the MAC that was previously generated and if they

are equal then the information has not been altered.

The MAC as specified in ANSI X9.9 is computed in the same manner as the data

authentication code (DAC) specified in FIPS PUB 1 13. Similarly, the Data

Identifier (DID) speciified in FIPS PUB 1 13 is sometimes referred to as a

Message Identifier (MID) in standards related to message communications.

4.1.2.1. THE DAA Authentication Process

Applying the DAA to data generates a DAC. The DAC, which is a mathematical

function of both the data and a cryptographic key, may then be stored, or

transmitted, with the data. When the integrity of the data is to be verified, the

DAC is generated on the current data and compared with the previously

generated DAC. If the two values are equal, the integrity (i.e., authenticity) of the

data is verified.

The DAA detects data modifications that occur between the initial generation of

the DAC and the validation of the received DAC. It does not detect errors that occur before the DAC is originally generated.

^® The information in this section was extracted from FIPS PUB 113.

27
Implementing Cryptography

The integrity provided by the DAA is based on the fact that it is infeasible to

generate a DAC without knowing the cryptographic l<ey. An adversary without

knowledge of the key will not be able to modify data and then generate an

authentic DAC on the modified data. It is therefore crucial that keys be protected

so that their secrecy is preserved.

4.2. Hash Functions

A hash function compresses the bits of a message to a fixed-size hash value in a

way that distributes the possible messages evenly among the possible hash

values. A cryptographic hash function does this in a way that makes it extremely

difficult to come up with a message that would hash to a previously computed

hash value.

4.2.1. SHAand

The Secure Hash Algorithm (SHA-1) can be used to generate a condensed

representation of a message called a message digest. When a message of any

length < 2^^ bits is input, the SHA-1 produces a 160-bit message digest. The

message digest can then be input to the Digital Signature Algorithm (DSA) which

generates or verifies the signature for the message. Signing the message digest

rather than the message often improves the efficiency of the process because

the message digest is usually much smaller in size than the message. The same

hash algorithm must be used by the verifier of a digital signature as was used by

the creator of the digital signature.

The SHA-1 is called secure because it is computationally infeasible to find a

message which corresponds to a given message digest, or to find two different

messages which produce the same message digest. Any change to a message

in transit will, with very high probability, result in a different message digest, and

the signature will fail to verify. SHA-1 is a technical revision of SHA^^. The SHA1 is based on principles similar to those used by Professor Ronald L. Rivest of

MIT when designing the MD4 message digest algorithm ("The MD4 Message

Digest Algorithm," Advances in Cryptology - CRYPTO '90 Proceedings, SpringerVerlag, 1991, pp. 303-311), and is closely modeled after that algorithm.

SHA-1 is required for use with the DSA as specified in the Digital Signature

Standard (DSS) and whenever a secure hash algorithm is required for Federal

applications.

The information is this section was extracted from FIPS PUB 180-1

.

A circular left shift operation has been added to the specifications in section 7,

line b, page 9 of FIPS PUB 180 and its equivalent in section 8, line c, page 10 of

FIPS PUB180. This revision improves the security provided by this standard.

28
Implementing Cryptography

The SHA-1 may be used with the DSA in electronic mail, electronic funds

transfer, software distribution, data storage, and other applications that require

data integrity assurance and data origin authentication. The SHA-1 may also be

used whenever it is necessary to generate a condensed version of a message.

4.3. Asymmetric Key Cryptography

The main problem with symmetric key cryptography is getting the sender and

receiver to agree on the secret key without anyone else finding out. If they are in separate physical locations they must trust a courier, or a phone system, or some

other transmission medium to prevent the disclosure of the secret key being

communicated.

The concept of public-key cryptography was introduced in 1976 by Whitfield

Diffie and Martin Hellman [DH76] in order to solve the key management problem.

In their approach, each person gets a pair of keys, one called the public key and

the other called the private key. Each person's public key is published while the

private key is kept secret. All communications involve only public keys, and no

private key is ever transmitted or shared. The only requirement is that public

keys are associated with their users in a trusted (authenticated) manner. Anyone

can send a confidential message by using only the public information, but the

message can only be decrypted with a private key, which is in the sole

possession of the intended recipient.

4.3.1. Digital Signatures

A digital signature is an electronic analogue of a written signature in that the

digital signature can be used in proving to the recipient or a third party that the

message was, in fact, signed by the originator. Digital signatures may also be

generated for stored data and programs so that the integrity of the data and

programs may be verified at any later time.

Digital signatures authenticate the integrity of the signed data and the identity of

the signatory. Digital signatures may also be used in proving to a third party that

data was actually signed by the generator of the signature. Digital signatures are intended for use in electronic mail, electronic funds transfer, electronic data

interchange, software distribution, data storage, and other applications that

require data integrity assurance and data origin authentication.

A digital signature is represented in a computer as a string of binary digits and is computed using a set of rules and a set of parameters such that the identity of

the signatory and integrity of the data can be verified. An algorithm provides the

capability to generate and verify signatures. Signature generation makes use of a private key to generate a digital signature. Signature verification makes use of a public key which corresponds to, but is not the same as, the private key. Each

user possesses a private and public key pair. Anyone can verify the signature of

29
Implementing Cryptography

a user by employing that user's public key. Signature generation can be

performed only by the possessor of the user's private key. The security of a

digital signature system is dependent on maintaining the secrecy of users' private

keys. Users must, therefore, guard against the unauthorized acquisition of their

private keys.

A hash function is used in the signature generation process to obtain a

condensed version of data, called a message digest (see Figure 3). The

message digest is then input to the digital signature (ds) algorithm to generate

the digital signature. The digital signature is sent to the intended verifier along

with the signed data (often called the message). The verifier of the message and

signature verifies the signature by using the sender's public key. The same hash

function must also be used in the verification process. Similar procedures may

be used to generate and verify signatures for stored as well as transmitted data.

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31
Implementing Cryptography

A digital signature can also be used to verify that information has not been

altered after it was signed; this provides message integrity.

The non-repudiation property of a digital signature relies on the mathematical

assumption that it is computationally infeasibie to derive the private key from the

public key and/or a set of messages and signatures prepared using the private

key. The non-repudiation property of a digital signature also relies on the

practical assumption that the private key is, or can be, associated with a single

entity (the signer), that only the signer has knowledge of or use of the private

key, and that the private key can and will be kept secret.

Digital signatures offer protection not available by alternative signature

techniques. One such alternative is a digitized signature. A digitized signature is generated by converting a visual form of a handwritten signature to an electronic

image. Although a digitized signature resembles its handwritten counterpart, it does not provide the same protection as a digital signature. Digitized signatures

can be forged. They can also be duplicated and appended to other electronic

data. Digitized signatures cannot be used to determine if information has been

altered after it is signed.

4.3.1 .1 . Digital Signature Standard (DSS)^^

FIPS PUB 186-2, Digital Signature Standard (DSS), is based on public key

cryptography which makes use of two keys: a public key and a private key. The

DSS specifies a digital signature for use in computing and verifying digital

signatures. DSS includes three digital signature algorithms: DSA, RSA and

Elliptic Curve Digital Signature Algorithm (ECDSA). The DSS is used in conjunction with FIPS PUB 180-1, Secure Hash Algorithm.

FIPS PUB 186-2 allows for the use of DSA, ANSI X9.31 {Digital Signatures Using

Reversible Public Key Cryptography for the Financial Sen/ices Industry (rDSA)),

and ANSI X9.62 {Public Key Cryptography for the Financial Services Industry:

The Elliptic Curve Digital Signature Algorithnri). The ANSI X9.31 standard

describes the Rivest-Shamir-Adleman (RSA) digital signature technique.

FIPS PUB 186-2 reflects the availability of conformity testing for DSA

implementations. (ANSI's conformity testing programs for ANSI X9.31 and ANSI

X9.62 implementations are not yet in place.)

Separate keys should be used for signature and confidentiality purposes when

using the ANSI X9.31 standard. This is because the RSA algorithm can be used

for both data encryption and digital signature purposes. To minimize any

potential for spoofing digital signatures, keys used for signature purposes should

The information in this section was extracted from FIPS PUB 186-2.

32
Implementing Cryptography

not be recoverable. Using separate keys will allow agencies to recover

confidentiality keys but not signature keys.

Digital Signature Algorithm (PSA)

DSA is used by a signatory \o generate a digital signature on data and by a

verifier \o verify the authenticity of the signature. Each signatory has a public and

private key. The private key is used in the signature generation process and the

public key is used in the signature verification process. The private key is randomly generated and is kept secret. Its owner should control its use and it should be protected against modification as well as disclosure. Using this key

and a mathematical process defined in the standard, the public key is generated.

The public key can be known by anyone; however, no one should be able to

modify it. DSA must be used in designing and implementing public-key based signature

systems that Federal departments and agencies operate or which are operated

for them.

Digital Signature Process

The DSA is used with SHA-1 to generate and verify digital signatures. To

generate a signature on a message, the owner of the private key first applies the

SHA-1 to the message. This action results in a message digest. The owner of

the private key then applies the private key to the message digest using the

mathematical techniques specified in the DSA to produce a digital signature.

Any party with access to the public key, message, and signature can verify the

signature using the DSA. If the signature verifies correctly, the receiver (or any

other party) has confidence that the message was signed by the owner of the

public key and the message has not been altered after it was signed.

In addition, the verifier can provide the message, digital signature, and signer's

public key as evidence to a third party that the message was, in fact, signed by

the claimed signer. Given the evidence, the third party can also verify the

signature. This capability, an inherent benefit of public key cryptography, is called non-repudiation. The DSS does not provide confidentiality of information.

If confidentiality is required, the signer could first apply the DES to the message

and then sign it using the DSA.

A means of associating public and private key pairs to the corresponding users is required. That is, there must be a binding of a user's identity and the user's

public key. This binding may be certified by a mutually trusted party. For

example, a certifying authority could sign credentials containing a user's public

key and identity to form a certificate.

33
Implementing Cryptography

Applications of Digital Signatures. Because the DSA authenticates both the

identity of the signer and the integrity of the signed information, it can be used in a variety of applications. For example, the DSA could be utilized in an electronic

mail system. After a party generated a message, that party could sign it using

the party's private key. The signed message could then be sent to a second

party. After verifying the received message, the second party would have

confidence that the message was signed by the first party. The second party

would also know that the message was not altered after the first party signed it.

The DSA could also be useful in the distribution of software. A digital signature

could be applied to software after it has been validated and approved for

distribution. Before installing the software on a computer, the signature could be

verified to be sure no unauthorized changes (such as the addition of a virus)

have been made. The digital signature could be verified periodically to ensure

the integrity of the software.

Random Number Generation

To use the DSA, a party must be able to generate random numbers to produce

the public/private key pair and to compute the signature. Random numbers can

be generated either by a true noise hardware randomizer or by using a

pseudorandom number generator. Approved random number generators are found in Appendix 3 of FIPS PUB 186 and Appendix C of ANSI X9.17, Financial

Institution Key Management (Wholesale). Random numbers are used to derive a

user's private key, x, and a user's per-message secret number, k. These values

are used in the DSA. The randomly or pseudorandomly generated integers are

selected to be between 0 and the 160-bit prime q (as specified in the standard).

rDSA^°

Digital Signatures Using Reversible Public Key Cryptography For The Financial

Sen/ices Industry (rDSA), is a technique for generating and validating digital

signatures. When implemented with proper controls, the techniques will provide the

ability to determine:

- data integrity, and

- non-repudiation of the message origin and contents.

Additionally, rDSA provides the ability to detect duplicate messages and prevent

the acceptance of replayed messages when the signed message includes:

1 . The identity of the intended recipient, and

2. A message identifier (MID).

The information in this section was extracted from ANSI X9.31

.

34
Implementing Cryptography

The MID should not repeat during the cryptoperiod of the underlying private/public

key pair.

The standard, adapted from ISO/IEC 9796-2 [2] and ISO/IEC 14888-3 [16], defines

a method for digital signature generation and verification for the protection of

financial messages and data using reversible public key cryptography systems

without message recovery. In addition, rDSA provides the criteria for the

generation of public and private keys required by the algorithm and the procedural

controls required for the secure use of the algorithm.

For both signature generation and verification, the data that is referred to in this

standard as a message, M, is reduced by means of a hash algorithm. Also, there

must be a reliable binding of a user's identity and the user's public key. This

binding may be accomplished by a mutually trusted party in the formulation of a

public key certificate using a CA.

rDSA includes:

- Key generation. The outputs from key generation are a public verification

key and a private signature key.

- Signature process. The signature generation process consists of the

following steps: message hashing, hash encapsulation, signature

production, and signature validation (optional).

Verification process. The signature verification process consists of the

following steps: signature opening, encapsulated hash verification, hash

recovery, and message hashing and comparison.

For rDSA, the integrity of signed data is dependent upon:

1. The prevention of unauthorized disclosure, use, modification, substitution,

insertion and deletion of d (private signature exponent), p and q (private

prime factors), or seeds.

2. The prevention of unauthorized modification, substitution, insertion and

deletion of e (public exponent) and n (public modulus).

The primes p and q (the factors of the modulus n) must be kept secret or destroyed. If the private signature exponent, d, or the seeds are disclosed, the

integrity of any message signed using that dean no longer be assured. Also, key

generation should be protected from unauthorized access to prevent disclosure

of sensitive keying material. Using the same seeds will produce the same keying

material that may have been compromised.

An Overview of Elliptic Curve Schemes

Many public-key cryptographic schemes are based on exponentiation operations

in large finite mathematical groups. The cryptographic strength of these

35
Implementing Cryptography

schemes is derived from the believed computational intractability of computing

logarithms in these groups. The algebraic system defined on the points of an

elliptic curve provides an alternate means to implement cryptographic schemes

based on the discrete logarithm problem. The primary advantage of elliptic curve schemes is their apparent high cryptographic strength relative to the key size.

Elliptic curve systems are public-key (asymmetric) cryptographic algorithms that are typically used to:

1 . Create digital signatures (in conjunction with a hash algorithm), and

2. Establish secret keys securely for use in symmetric-key cryptosystems.

Elliptic Cun/e Digital Signature Algorithm (ECDSA)^^

The Elliptic Curve Digital Signature Algorithm {ECDSA) defines a technique for

generating and validating digital signatures. ECDSA is the elliptic curve analogue of DSA. The ECDSA must be used in conjunction with the hash

function SHA-1.

When implemented with proper controls, ECDSA provides data integrity, data

origin authentication, and non-repudiation of the message origin and the

message contents. Additionally, when used in conjunction with a MID, ECDSA

provides the capability of detecting duplicate transactions.

The ECDSA is used by a signatory \o generate a digital signature on data and by

a verifier to verify the authenticity of the signature. Each signatory has a public

and private key. The private key is used in the signature generation process,

and the public key is used in the signature verification process. For both

signature generation and verification, the message, M, is compressed by means

of the SHA-1 prior to the signature generation and verification process.

Control of Keying Material: The signatory must provide and maintain the proper

control of all keying material. In the ECDSA asymmetric cryptographic system,

the integrity of signed data is dependent upon:

1 . the prevention of unauthorized disclosure, use, modification, substitution,

insertion, and deletion of the private key, d, the per-message value, k, and

(optional) seeds input to their generation, and

2. the prevention of unauthorized modification, substitution, insertion, and

deletion of elliptic curve parameters for the ECDSA computation

procedures (see Section 5.1 of ANSI X9.62).

The information in this section was extracted from ANSI X9.62.

36
Implementing Cryptography

If dis disclosed, the integrity of any message signed using that dean no longer

be assured. Similarly, the values for the elliptic curve parameters must be

protected.

(Note: Key generation should be performed on physically isolated equipment so

that in the event of a hardware or software failure, no partial information is retained. For example, if a system crash causes a core dump, some of the

keying material data may be captured.)

ECDSA includes:

- Key generation,

- Key validation,

- Signature generation, and

- Signature verification.

4.3.2. Key Transport/Agreement

Key management is extremely important because the security of any

cryptographic system is dependent on the security provided to the cryptographic

keys. For a cryptographic system to work effectively, keys must be generated,

distributed, used, and destroyed securely. Key management is an issue in both

secret key systems and public key systems.

Symmetric schemes such as the DEA provide services such as data integrity and

data confidentiality. However, the major drawback with the implementation of

such schemes is that any two communicating entities must establish in advance

a shared secret key. As the size of a system or the number of entities using a

system increases this can lead to a key management problem.

An attractive solution to this key management problem is for a system to employ

asymmetric techniques that allow any pair of entities to establish a shared secret

key suitable for use by a symmetric scheme despite the fact that the two entities

may never have previously engaged in a secure communications together. Such

asymmetric techniques are known as asymmetric key establishment schemes.

4.3.2.1. RSA^^

Employing public key cryptography for the management of symmetric keys

requires sound public key pair generation, key transport and key agreement.

The information in this section was extracted from draft ANSI X9.44. Because

this standard is in draft form, the information presented in this section is subject

to revision.

37
Implementing Cryptography

ANSI X9.44, The Transport of Symmetric Algorithm Keys Using Reversible

Public Key Cryptography, is a draft standard for secret key transport based on

the RSA algorithm. The RSA and Rabin-Williams asymmetric algorithms are well

understood and widely implemented public key techniques that facilitate costeffective key management across modern networks, such as the Internet. RSA

gets its security from the difficulty of factoring large numbers. The public and

private keys are functions of a pair of large (100 to 200 digits or even larger)

prime numbers.

The standard defines mechanisms for managing symmetric cryptographic keys

using reversible public key cryptography. The standard also addresses the

security requirements and additional considerations when implementing key

management in combination with digital signatures in a PKI. The techniques

specified in the standard are designed to facilitate the secure establishment or secure transportation of symmetric keys.

Key Generation: the outputs from key generation are:

1 . a public verification key.

2. a private signature key.

Although each of the private signature key outputs are optional, enough

information must be retained to regenerate d, the private signature exponent,

for signature generation.

7 3. (Optional) audit information.

Key Transport is a mechanism whereby one party (the sender) generates a

random symmetric key and transports the symmetric key encrypted using the

public key of another party (the receiver). Key Transport using reversible public

key cryptography consists of the following steps:

1 . Symmetric key generation,

2. Symmetric key encryption, and

3. Symmetric key recovery.

Key Agreement is a mechanism whereby two parties actively share in the

establishment of a random symmetric key without either party actually

exchanging the symmetric key. Key Agreement using reversible public key

cryptography consists of the following steps:

1 . Symmetric key component generation,

2. Symmetric key component encryption,

3. Symmetric key component recovery, and

4. Symmetric key derivation.

38
Implementing Cryptography

4.3.2.2. Elliptic Curve Key Agreement and Transport Protocols^^

ANSI X9.63 defines key establishment schemes that employ asymmetric

techniques. Both key agreement and key transport schemes are specified. The

arithmetic operations involved in the operation of the schemes take place in the

algebraic structure of an elliptic curve over a finite field. The schemes may be

used to compute shared keying data which may then be used by symmetric

schemes to provide cryptographic services like data confidentiality and data

integrity. The fundamental goal of any key establishment scheme is to distribute

keying data. Ideally, the keying data should have precisely the same attributes as keying data established face-to-face. It should be randomly distributed, and

no unauthorized entity should know anything about the keying data.

The asymmetric key establishment schemes in ANSI X9.63 are used by an entity

(7 who wishes to establish a symmetric key with another entity V. Each entity

has an elliptic curve (EC) key pair. If U and 1/ simultaneously execute a scheme

with corresponding keying material as input, then at the end of the execution of

the scheme, L/and \/will share keying data that can be used by symmetric

algorithms.

ANSI X9.63 specifies a variety of asymmetric key establishment schemes. Each

of the mechanisms, when implemented securely and embedded within a

cryptographic system in an appropriate manner, is capable of providing two

entities with a shared secret key suitable for use in symmetric algorithms like the

DEA. A variety of schemes is specified because of the wide variety of services

that it may or may not be desirable for a key establishment scheme to provide

depending on the environment in which the scheme is going to be used. The

schemes in this Standard employ other cryptographic transformations in their

operation. The transformations used are: DEA, DEA-based MAC, SHA-1 , and

the ECDSA.

Implementing the Schemes Securely

Two common prerequisites for the implementation of schemes in ANSI X9.63 are

that all entities involved in the use of the schemes are provided with an authentic

copy of the elliptic curve parameters being used and that every entity is provided

with a genuine copy of every other entity's static public key. The latter binding

between an entity and its static public key may be accomplished by using a

Certification Authority.

The information in this section was extracted from draft ANSI X9.63. Because

this standard is in draft form, the information presented in this section is subject

to revision.

39
Implementing Cryptography

However, satisfying the stated prerequisites is not enough to ensure the security

of an implementation. The secure implementation of the schemes in ANSI X9.63

is also dependent upon:

1 . The prevention of unauthorized disclosure, use, modification, substitution,

insertion, and deletion of an entity's static private key di,

2. The prevention of unauthorized modification, substitution, insertion, and

deletion of the elliptic curve parameters being used;

3. The secure implementation of the transformations involved in an execution

of a scheme so that the integrity and confidentiality of the computations

involved is maintained.

Note that this includes the secure destruction of any ephemeral values involved

in the operation of a scheme. Any implementation must also provide explicit key

authentication of any session key established using one of the key establishment

schemes. Finally, secure implementation of the schemes does not guarantee the

security of the operation of the implementation. It is the responsibility of the

operator to put an overall process in place with the necessary controls to ensure

the secure operation.

Key Agreement Schemes

The key agreement scheme is used by an entity U who wishes to agree keying

data with an entity V. In some cases, the protocols specified are "symmetric,"

and so it suffices to describe just one transformation. In other cases, the

protocols are "asymmetric," and so it is necessary to describe two

transformations, one of which is undertaken by L/if U \s the initiator, and one of

which is undertaken by U \i U is the responder. In the specification of each

transformation, equivalent computations that result in identical output are

allowed.

Key Transport Schemes

The key transport scheme is used by an entity U who wishes to establish keying

data with an entity V. Both protocols specified are 'asymmetric', so it is necessary to describe two transformations, one of which is undertaken by if 1/

is the initiator, and one of which is undertaken by L/ if U is the responder. In the

specification of each transformation, equivalent computations that result in identical output are allowed.

40
Implementing Cryptography

4.3.2.3. Agreement of Symmetric Keys Using Discrete Logarithm

Cryptography^"*

The Diffie-Hellman and MQV key agreement protocols (also called exponential

key agreement) allows two users to exchange a secret key over an insecure

medium without any prior secrets. This secret key can then be used to encrypt

further communications between the parties. The protocols depend on the

discrete logarithm problem for their security. The basic versions provide

protection in the form of secrecy of the resulting key from passive adversaries

(eavesdroppers), but not from active adversaries capable of intercepting,

modifying, or injecting messages.

The basic algorithms used to calculate a shared secret number are the DiffieHellman algorithm and the MQV algorithm. A cryptographic key will be derived

from the shared secret number by using a key derivation function. The key

derivation function must be a one-way hash function. The default hash function

is SHA-1.

Key Agreement Using the Diffie-Hellman Algoritlim

dhStatic : Each party has only static data available. Individual static

private/public key pairs are generated using the same set of static key

domain parameters.

dhEphem : Each party has only ephemeral data available. Individual

ephemeral private/public key pairs are generated using the same set of

ephemeral key domain parameters.

dhOneFlow: One party has only static data and the other party has only

ephemeral data. Two private/public key pairs are generated using the

same domain parameters.

dhHybridl : Each party has two pairs of private/public keys: one key pair is static and another is ephemeral. Two private/public pairs are generated

using the same domain parameters.

dhHvbrid2 : Each party has two pairs of private/public keys: one pair is static

and the other is ephemeral. The static key pair is generated using a set of

static key domain parameters. The ephemeral key pair is generated using

a set of ephemeral key domain parameters.

The information in this section was extracted from draft ANSI X9.42. Because

this standard is in draft form, the information presented in this section is subject

to revision.

41
Implementing Cryptography

dhHvbridOneFlow: One party has both a static and an ephemeral

private/public key pair and the other party has one static private/public key

pair. All of the key pairs are generated using the same domain

parameters.

Key Agreement Using the MQVAlgorithm

MQV2: Each party has two pairs of private/public keys: one pair is static and

the other is ephemeral. Individual static and ephemeral private/public key

pairs are generated using the same domain parameters.

MQV1 : Two parties contribute different amounts of information and use

different algorithms to obtain the common shared secret value. Party A

has two pairs of private/public keys. One key pair is static and the other

key pair is ephemeral. Party B has one private/public key pair that is static.

4.3.2.4. Key Exchange Algorithm (KEA)

KEA is a key exchange algorithm. All calculations for KEA require a 1024-bit

prime modulus. This modulus and related values are to be generated as per the

DSS specification. The KEA is based upon a Diffie-Hellman protocol utilizing

SKIPJACK to reduce final values to an 80-bit key. The KEA provides security

commensurate with that provided by SKIPJACK, on the order of 2^° operations.

KEA requires that each user be able to validate the public values received from

others, but does not specify how that is to be done.

4.4. Key Management^®

FIPS PUB 171 , along with ANSI X9.17, provides a key management system for:

- a Point-to-Point environment in which each party to a key exchange

shares a key encrypting key which is used to distribute other keys

between the parties,

- a Key Distribution Center environment in which each party shares a key

encrypting key with a center who generates keys for distribution and use

between pairs of parties, and

- a Key Translation Center environment in which each party shares a key

encrypting key with a center who translates keys generated by one party

which will be distributed to another party, the ultimate recipient.

The information in this section was extracted from FIPS PUB 171 and ANSI

X9.17.

42
Implementing Cryptography

ANSI X9. 17-1 985, Financial Institution Key Management (Wholesale), is a

voluntary industry standard that defines procedures for the manual and

automated management of the data (e.g., keys and initialization vectors)

necessary to establish and maintain cryptographic keying relationships. It defines the protocols to be used by financial institutions, such as banks, to

transfer encryption keys. This protocol is aimed at the distribution of secret keys

using symmetric (secret-key) techniques. This data is known as keying material.

ANSI X9.17 specifies the minimum requirements for:

- Control of the keying material during its lifetime to prevent unauthorized

disclosure, modification or substitution;

- Distribution of the keying material in order to permit interoperability

between cryptographic equipment or facilities;

- Ensuring the integrity of keying material during all phases of its life, including its generation, distribution, storage, entry, use and destruction;

and

- Recovery in the event of a failure of the key management process or when

the integrity of the keying material is questioned.

ANSI X9.17 utilizes DES to provide key management solutions for a variety of

operational environments. As such, ANSI X9.17 contains a number of options.

Systems which are built to conform to all options of ANSI X9.17 are likely to be

complex and expensive. FIPS PUB 171 adopts ANSI X9. 17-1985 and specifies

a particular selection of options for the automated distribution of keying material

by the Federal government using the protocols of ANSI X9.17. In FIPS PUB 171

each option is numbered and listed, its use in ANSI X9.17 is described, the

selection for Federal government use is specified along with any other additional

requirements, and a brief justification for the selection is provided. The options

selected were chosen with regard to the degree of cryptographic protection that

can be provided for the data with which the keys will be used, as well as a

decision to reduce the complexity and cost of ANSI X9.17 implementations by

limiting the number of options which are implemented and tested.

43
Implementing Cryptography

CHAPTER 5

5. PUBLIC KEY INFRASTRUCTURE (PK\f^

Public key cryptography can play an important role in providing needed security

services including confidentiality, authentication, digital signatures, and integrity.

This chapter includes an overview of a Public Key Infrastructure (PKI), a

discussion of alternative PKI architectures, interoperability and policy issues, a

description of the Minimum Interoperability Specification for PKI Components

(MISPC), and the Federal government PKI.

5.1. Public Key Infrastructure (PKI) Overview

A PKI provides the means to bind public keys to their owners and helps in the

distribution of reliable public keys in large heterogeneous networks. Public keys

are bound to their owners by public key certificates. These certificates contain

information such as the owner's name and the associated public key and are issued by a reliable CA.

The basic components of a PKI are:

Public Key Certificate - An electronic record that binds a public key to the

identity of the owner of a public-private key pair and is signed by a trusted

entity. Public key certificates are the mechanism for describing trust relationships in a PKI. Certificates may be issued to CAs or other end

entities. Certificates issued to CAs indicate the certificate holder is trusted

to issue additional certificates. Certificates issued to other end entities are

appropriate for provisioning other security services, but are not trusted for

issuing additional certificates. Certificates include an expiration date.

However, if the CA ceases to trust the certificate holder before certificate

expiration, the CA must revoke the certificate.

Certificate Revocation List (CRL) - A list of certificates that have been

revoked. The list is usually signed by the same entity that issued the

certificates. Certificates can be revoked for several reasons. For

example, a certificate can be revoked if the owner's private key has been

lost; the owner leaves the company/agency; or the owner's name

changes. CRLs also provide an important mechanism for documenting

the historical revocation status of certificates. That is, a dated signature

may be presumed to be valid if the signature date was within the validity

period of the certificate, and the current CRL of the issuing CA at that date

did not show the certificate to be revoked.

The information in this section was extracted from unpublished papers

developed by W. E. Burr, D. F. Dodson, N. A. Nazario, and W. T. Polk of NIST.

44
Implementing Cryptography

CA - A trusted entity that issues and revokes public key certificates and

certificate revocation lists.

Registration Auttiority (RA) - An entity that is trusted by the CA to register or vouch for the identity of users to a CA.

Certificate Repository - An electronic site that holds certificates and CRLs.

CAs post certificates and CRLs to repositories.

Certificate User - An entity that uses certificates to know, with certainty,

the public key of another entity.

Certificate Holder - An entity that is issued a certificate and can sign digital

documents.

Clients - Entities that validate digital signatures and their certification paths

from a known public key of a trusted CA.

5.2. PKI Architectures

A PKI is often composed of many CAs linked by trust paths. The CAs may be

linked in several ways. They may be arranged hierarchically under a "root CA"

that issues certificates to subordinate CAs. The CAs can also be arranged

independently in a mesh^''. Recipients of a signed message with no relationship

with the CA that issued the certificate for the sender of the message can still validate the sender's certificate by finding a path between their CA and the one

that issued the sender's certificate. Figures 4 and 5 illustrate the two basic PKI

architectures.

Bob

Figure 4. Mesh Architecture

A mesh PKI model is sometimes referred to as a network PKI model.

45

1
Implementing Cryptography

Bob

Figures. Hierarchical Architecture

in hierarchical models, trust is delegated by a CA when it certifies a subordinate

CA. Trust delegation starts at a root CA that is trusted by every node in the

infrastructure. In mesh models, trust is established between any two CAs in peer

relationships (cross-certification), thus allowing the possibility of multiple trust paths between any two CAs.

5.3. Security Policies of Other CAs and the Network

It is important to consider the integrity and security of the PKI components. The

confidence that can be placed in the binding between a public key and its owner

depends much on the confidence that can be placed on the system that issued

the certificate that binds them. The rules expressed by certificate policies are

reflected in certification practice statements (CPSs) that detail the operational

rules and system features of CAs and other PKI components. By examining a

CA's CPS, users can determine whether to obtain certificates from it, based on

their security requirements. Other CAs can also use the CPS to determine if they

want to cross-certify with that CA. The essential issue with cross-certificates is how to allow CAs to cross-certify with other CAs to meet the particular needs of

their own users, without compromising the security of users of other CAs. For

example, a particular agency might have a close working relationship with a local

government office, a particular contractor or law firm that has its own CA. That

relationship, however, would not necessarily justify extension of trust to other

government agencies or commercial organizations.

5.4. Interoperability

To be useful in a global sense, PKI components need to interoperate regardless

of the source of the equipment and the software involved. PKI technology

promises to deliver security services across user communities, even where

business partners have not met face to face. However, the current PKI products

and services fall somewhat short of this promise, and interoperability is one

major factor. For example, incompatible transaction protocols and certificate

46
Implementing Cryptography

formats prevent implementation of heterogeneous PKIs. PKI components from

different vendors may be unable to communicate. PKI users may find they can

communicate, but cannot process each other's certificates.

Although there have been several proposed formats for public key certificates,

most certificates available today are based on an international standard (ITU-T

X.509 version 3). This standard defines a certificate structure that includes

several optional extensions. The use of X.509v3 certificates is important

because it provides interoperability between PKI components. Also, the

standard's defined extensions offer flexibility to support specific business needs.

If a community identifies additional information that is not covered by the

standard extensions, they can define it and include it in their certificates or CRLs

without violating the current format.

Impediments to interoperability remain, however. The number of standard

extensions is relatively large, and vendors are struggling to prioritize their

implementation. When a certificate is issued, extensions may be marked as

"critical" or "non-critical." If an extension is critical, a product must recognize and

process the extension or reject the certificate. If users have certificates with

critical extensions that are not broadly supported in products, they will not be

able to provision services with other users. In addition, many extensions are broadly defined. The content and semantics of the extensions are unclear, so two PKI products may interpret them differently.

5.5. Minimum Interoperability Specification for PKI Components (MISPC)

To enhance interoperability of Commercial-Off-The-Shelf (COTS) products, NIST

recently completed the development of a Minimum Interoperability Specification

for PKI Components, version 1 (MISPC). The MISPC was produced in cooperation with ten industry partners through Cooperative Research and

Development Agreements (CRADAs) and provides a basis for interoperable PKI

components from different vendors. The MISPC focuses primarily on the

aspects of PKI interoperation most apparent to end users, that is, how to request

and be issued a certificate, how to sign documents, how to retrieve the

certificates of others, and how to validate signatures.

The goal of the MISPC is to further interoperability among heterogeneous public

key certificate management systems, thus enabling large user communities to

take advantage of digital signature technology. Transactions for issuing,

revoking and managing public key certificates are defined in the specification.

These transactions support the use of digital signatures as a replacement for

The participating companies were: AT&T; Bolt Beranek Newman (BBN);

Certicom; Cylink; DynCorp; Entrust Technologies (Northern Telecom);

Information Resources Engineering (IRE); Motorola; Spyrus, Inc.; and VeriSign,

Inc.

47
Implementing Cryptography

handwritten signatures and as a reliable authentication mechanism. This is sufficient to meet two basic goals of interoperability. First, conforming products

and services can be mixed to build a heterogeneous PKI. Second, users with

conforming certificates can establish the trust relationships required to use

signatures and perform authentication.

The MISPC is based on the use of X.509v3 certificates and v2 CRLs. The

specification includes a certificate profile that enumerates support and use of the

standardized certificate extensions. It provides specifications for the five PKI

components: Certificate Authorities, Registration Authorities, Repositories,

Certificate Holders (which hold certificates and can sign documents) and Clients

(which validate signatures). The MISPC includes protocols for issuing and

revoking certificates and retrieving them from repositories and supports the use

of digital signature certificates and recognizes three digital signature algorithms

including: DSA, ECDSA and RSA with SHA-1 message digests.

The MISPC supports both mesh and hierarchical and trust models, as shown in Figures 5 and 6 and assumes that X.509v3 extensions will be included in certificates to explicitly manage trust relationships. The MISPC assumes that

certificates and CRLs are available in a repository for retrieval without

authentication. MISPC clients can perform path validation by obtaining the

necessary certificates and CRLs from the appropriate repositories.

5.6. Federal PKI Architecture

Currently, there are many efforts in Federal agencies to set up independent CAs

to support individual applications. In general, an application that supports the

agency mission, such as purchasing, grants, or travel pays for operating the CA.

For these applications, the use of public key technology must be justified in terms

of its direct benefit to a specific agency application. Alternatively, the Federal

government may use commercial CA service providers to issue certificates and

facilitate delivering services. The various agency projects that rely upon these

certificates will pay the commercial CA service provider.

Broader government-wide PKI needs and associated systems do not generally

facilitate interagency operation, or the creation of a broader national PKI. The

main issue for the Federal PKI is how to create certification paths between

Federal agencies that will provide for reliable and broad propagation of trust. A

Bridge CA (BCA) provides systematic certification paths between CAs in agencies, and outside the government. Federal CAs that meet certain standards

and requirements will be eligible to cross-certify with the BCA, thereby gaining

the certification paths needed for broad trust interoperation in the Federal and

national PKI. While the certification path processing limitations of some less

functional clients may confound interoperability at times, the existence of these

certification paths is a necessary precondition for broad trust interoperation.

48
Implementing Cryptography

bridge CA ^—^ bridge cross certificate pair

® principal CA CA certificate

^

peer CA ^ *. cross certificate pair

O subordinate CA

Figure 6. Proposed Federal PKI Certification Path Architecture

5.6.1. Architecture Components

The certification path elements of the proposed architecture are illustrated in Figure 6. The complete architecture is composed of the following components:

• Federal Policy Management Authority (FPMA): this management authority

sets the overall policies of the Federal PKI, and approves the policies and

procedures of trust domains within the Federal PKI. It operates a Federal

Bridge CA, and repository.

• Trust Domains: In the Federal context, a trust domain is a portion of the

Federal PKI that operates under the management of a single policy

management authority. One or more CAs exist within each trust domain.

Each trust domain has a single principal CA, but may have many other CAs.

Each trust domain has a domain repository.

• Domain Policy Management Authory (DPMA): a policy management

authority approves the certification practice statements of the CAs within a

trust domain and monitors their operation. The DPMAs operate or supervise

49
Implementing Cryptography

a domain repository.

Certification Authorities (CA):

- Bridge CA (BCA): the Federal Bridge CA is operated by the FPMA. Its purpose is to be a bridge of trust that provide trust paths between the

various trust domains of the Federal PKI, as well as between the Federal

PKI and non-Federal trust domains. FPMA-approved trust domains

designate a principal CA that is eligible to cross-certify with the Federal

BCA. The BCA is not a root CA because it does not typically begin

certification paths.

- Principal CA: A CA within a trust domain that cross-certifies with the

Federal BCA. Each trust domain has one principal CA. In a domain with

hierarchical certification paths, it will be the root CA of the domain. In a

mesh organized domain, the principal CA may be any CA in the domain.

However it will typically be one operated by or associated with the DPMA.

- Peer CA: A CA in a mesh domain, the peer CA has a self-signed

certificate that is distributed to its certificate holders and used by them to

inititate certification paths. Peer CAs cross-certify with other CAs in their

trust domain.

- Root CA: In a hierarchical trust domain, the root CA is the CA that initiates

all trust paths. Certificate holders and relying parties are given the selfsigned root CA certificate by some authenticated means and all trust paths

are initiated from that point. For hierarchical trust domains, the root CA is also the principle CA for that domain.

- Subordinate CA: A CA in a hierarchical domain that does not begin trust paths. Trust initiates from some root CA. In a hierarchical trust domain, a

subordinate CA receives a certificate from it's superior CA. A subordinate

CA may have subordinate CAs of its own to which it issues certificates.

Repositories: Repositories are online facilities that provide certificates and

certificate status information. Repositories in the Federal PKI will provide

information via the LDAP protocol and may also provide information in other

ways. The FPMA will maintain an open LDAP repository for CA certificates

and revocations.

BCA Repository. The BCA repository will be open to internet access by

anyone via LDAP, and will provide the following: - All certificates issued by the BCA,

- All certificates held by the BCA,

50
Implementing Cryptography

- All cross certificate pairs containing certificates held or issued by the

BCA,

- The current CRL for all certificates issued by the BCA,

- Many or all CA certificates issued by CAs within the overall Federal

PKI as an aid to finding certification paths,

- Many or ail cross certificate pairs between CAs in the Federal PKI, and

- Other certificates and CRLs as determined by the FPMA.

• Certificate Status Responders (CSR): CSRs will use the emerging Internet

Online Certificate Status protocol to provide relying parties with an online, real

time response to the question, "Has this end entity certificate been revoked or suspended?" CSRs will only be used for end-entity certificates, which will be

the vast number of certificates in the Federal PKI. End-entity certificates will be changed and revoked much more frequently than CA certificates.

5.6.2. Operational Concept

The Federal BCA will be the unifying element to link otherwise unconnected

agency CAs into a systematic overall Federal PKI. The BCA is not a root CA. It does not begin certification paths, it simply connects trust domains through cross

certificate pairs to designated principal CAs. It is a bridge of trust. A FPMA will supervise BCA operation and establish the requirements for cross certifying with

the BCA. These trust domains may be within the government or outside the

government.

Federal (or non-Federal) CAs that operate in trust domains that meet the

requirements established by the FPMA will be eligible to cross certify with the

BCA. The BCA will then connect them to the overall trust network of the Federal

PKI. This will provide relying parties and certificate holders (in their trust domains) with connectivity to the larger Federal PKI. This will be simpler and

more effective than trying to manage an ad hoc collection of many cross

certifications with CAs in other trust domains.

To provide maximum flexibility to Federal agencies and not intrude upon their

prerogatives:

• Agencies will not be required to adopt the BCA's policies. Rather, agencies

will retain the option to use other policies defined by their own internal PMAs,

or by commercial certificate service providers.

• Agencies will not be required to use the BCA to interoperate with other

Federal agencies or organizations outside the Federal government.

51
Implementing Cryptography

Alternatively, Federal agencies may communicate directly with an

agency/organization to establish requirements for interoperating.

5.6.3. Federal PKI (FPKI) Steering Committee^^

The mission of the Federal PKI (FPKI) Steering Committee is to provide clear,

strong leadership within the U.S. Federal government during the development

and implementation phases of the Federal PKI. This committee consists of over

50 members from two dozen Federal agencies and will:

- Provide guidance and assist in the development of an interoperable public

key infrastructure that utilizes COTS standards-based products,

- Identify Federal government PKI requirements,

- Recommend policies, procedures and standards development activities

that support a Federal PKI,

- Provide oversight of PKI activities in Federal PKI pilot projects,

- Provide oversight and guidance on the establishment of key recovery

techniques,

- Specify technologies needed for a Federal PKI,

- Establish and maintain liaison with appropriate communities of interest,

- Establish interoperability and security requirements of products and

protocols related to the Federal PKI, and

- Make recommendations regarding establishment, demonstration, and

operation of a Federal PKI.

Information in this section is extracted from www.qits-sec.treas.qov,

52
Implementing Cryptography

CHAPTER 6

6. TESTING

Cryptographic sen/ices are provided using cryptographic modules

(cryptomodules), which may include capabilities such as signature generation

and verification (possibly involving key notarization), encryption and decryption,

key generation, key distribution, etc.

If a large number of cryptographic modules are needed to provide security

services in a system, then an undetected error in a cryptographic module's

design could potentially affect the performance of a cryptographic function for

every user in the system. For example, the verification of a chain of public key

certificates might not function correctly, or key notarization (for secret keys) might

be done improperly by a cryptomodule. Verifying a chain of public key

certificates helps a signature verifier determine if a signature was generated with a particular key. Likewise, key notarization helps ensure that no party other than

the signer of the data can use the data key to sign or encrypt information. If either of these functions were implemented incorrectly in a cryptomodule, the

potential for the dissemination of weak cryptography could be introduced into the

system, possibly allowing for signature forgery or the verification of invalid

signatures. Therefore, it is important to have all cryptographic modules tested

before distributing them throughout a system.

Figure 7 illustrates a general security testing model, including testing of

cryptographic modules, and the various levels of testing that are required. This

model, and the applicable testing organizations, is described in this chapter.

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At the lowest level are the cryptographic algorithms and cryptographic modules.

These must be tested prior to integration into an existing or new system. The

cryptographic modules are tested by the developer and then submitted to the

Cryptographic Module Validation Program (CMVP) for testing against FIRS PUB

1 40-1 , Security Requirements for Cryptographic Modules.

For all Federal agencies, including defense agencies, the use of encryption

products that conform to FIPS PUB 140-1 is mandatory for the protection of

sensitive unclassified information when the agency determines that cryptographic

protection is required^°. Agencies are required to use the standard in designing,

acquiring, and implementing cryptographic-based security systems within

computer and telecommunications systems (including voice systems).

6.1. Cryptographic Module Validation Program (CMVPf^

NIST and the Communications Security Establishment (CSE) of the government

of Canada established the CMVP. The goal of the CMVP is to provide Federal

agencies with a security metric to use in procuring equipment containing

cryptographic modules. The results of the independent testing, by accredited

laboratories, provide this metric. Cryptographic module validation testing is performed using the Derived Test Requirements (DTRs) for FIPS PUB 140-1.

The DTRs list all of the vendor and tester requirements for validating a

cryptographic module and are the basis of testing done by the Cryptographic

Module Testing (CMT) accredited laboratories. This section includes five

subsections: background information on the use of cryptographic modules, FIPS

PUB 140-1 requirements, validated modules list, implementation guidelines, and

testing requirements.

6.1.1. Background

A cryptographic module is a set of hardware, firmware or software, or some

combination that implements cryptographic logic or processes. Examples

include a standalone device such as a link encryptor, an add-on encryption board

embedded in a computer system, and a software application running on a

microprocessor such as a digital signature application. If the cryptographic logic

is implemented in software, then the processor, which executes the software, is also part of the cryptographic module.

There are many advantages to using validated modules:

- Assurance that modules incorporate necessary features.

National security-related information is excluded from this requirement.

The information in this section is extracted from FIPS PUB 140-1.

55
Implementing Cryptography

- Protection of technical assets and staff time of government personnel by

assuring that purchased products comply with a standard and have been

tested.

- Provide users with a set of available and relevant security features.

- Increase flexibility to choose security requirements that meet applicationspecific and environment-specific requirements.

Figure 8 illustrates the CMV process. The process begins with the submission of

the cryptographic module to one of the accredited laboratories. During the

testing process, there are typically many interactions between the laboratory and

the vendor and between the laboratory and NIST/CSE. NIST/CSE respond to

questions about a specific validation and issue general implementation guidance

that is applicable to all validations. The implementation guidance is not static,

and is augmented as needed to respond to questions. The laboratory then writes

the test report and submits it to NIST/CSE for validation. NIST/CSE review the

test report and request clarification from the laboratory, as required. Finally,

NIST/CSE issue the validation certificate and update the CMVP web site^^.

FIPS 140-1, DTRs, implementation guidance, and validated modules list data

are located at the web site: csrc.nist.qov/cn/ptval .

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In general, NIST/CSE responsibilities include:

- Reviewing reports and issuing validation certificates.

- Issuing CMVP policies.

- Issuing guidance and clarifications of FIPS PUB 140-1 and other

cryptography standards (to labs, vendors, government organizations,

and others).

- Assisting the National Voluntary Laboratory Accreditation Program

(NVLAP) in laboratory assessments.

6.1.2. FIPS PUB 140-1 Requirements

The security requirements in FIPS PUB 140-1 cover 1 1 areas related to the

design and implementation of a cryptographic module. Within most areas, a

cryptographic module receives a security level rating of 1-4, from lowest to

highest, depending on what requirements are met. For other areas that do not

provide for different levels of security, a cryptomodule receives a rating that

reflects fulfillment of all of the requirements for that area.

An overall rating is issued for the cryptomodule, which indicates:

(1) the minimum of the independent ratings received in the areas with levels,

and

(2) fulfillment of all the requirements in the other areas.

On a vendor's validation certificate, individual ratings are listed as well as the

overall rating. It is important for vendors and users of cryptographic modules to

realize that the overall rating of a cryptographic module is not necessarily the

most important rating. The rating of an individual area may be more important

than the overall rating, depending on the environment in which the cryptographic

module will be implemented (this includes understanding what risks the

cryptographic module is intended to address). Modules may meet different levels

in different security requirement areas; a module may implement identity-based

authentication (level 3 or 4) and display tamper evidence (level 2).

Table 2 lists the security requirements for cryptomodules. To illustrate the

various levels as described above, at Security Level 2, there are overall

requirements for cryptographic modules, cryptographic algorithms, and self-tests;

and specific requirements for roles and services and operating system security.

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6.1.3. Validated Modules List

The Validated Modules List includes the following information for each

cryptographic module:

- Vendor Name and Point-of-Contact (POC)

- Module Name and Version Number

- Module Type (software, hardware, firmware)

- Date of Validation

- Level(s) of Validation

- Description of Module (or products which incorporate this module)

A module on the list may be a product used in multiple products from that vendor

or used in another vendor's product(s).

6.1.4. Effective Use of HPS PUB 140-1

When implementing cryptography in a system:

- Examine FIPS PUB 140-1. Consider the requirements in each area. Determine those requirements that specify the features that are desired.

Determine those requirements (if any) specified in FIPS PUB 140-1 that

were not originally considered. Specify the appropriate level in each area

of the standard based on the acceptable level of risk.

- Obtain or develop cryptographic modules that meet or exceed the

selected levels.

6.2. National Voluntary Laboratory Accreditation Program (NVLAP)

The NIST National Voluntary Laboratory Accreditation Program (NVLAP)

accredits testing organizations based on technical accreditation requirements

and quality system requirements. NVLAP assesses the testing organization

against the NVLAP accreditation requirements to determine if the organization is competent to perform specific tests and calibrations. Competence is defined as

the ability of a laboratory to meet the NVLAP conditions and to conform to the

criteria in NVLAP publications for specific calibration and test methods.

6.3. Industry and Standards Organizations

The next higher level of testing, above algorithm and module testing, is at the

product level. Products are tested by the vendor, standards organizations, and

by independent verification and validation (IV&V) organizations. Vendors test

their products to ensure that they function properly and in a secure manner.

Cryptographic modules and components may be integrated or embedded into

60
Implementing Cryptography

these products. For government applications, the embedded cryptographic

modules must meet the requirements of FIPS PUB 140-1 . At this level of testing,

it is important to ensure that the product does not compromise or circumvent the

cryptographic features, resulting in a non-secure device. Currently, products

may be tested to the CC or to the Trusted Computer System Evaluation Criteria,

DOD-5200.28-STD.

6.3.1. National Information Assurance Partnership (NIAP)^^

The National Information Assurance Partnership (NIAP)®"^ is a U.S. Government

Initiative designed to meet the security testing needs of both information

technology producers and users. The program is intended to foster the

availability of objective measures and test methods for evaluating the quality of IT security products. In addition, it is designed to foster the development of

commercial testing laboratories that can provide the types of testing and

evaluation services which will meet the demands of both producers and users.

NIAP is a collaboration of NIST and the National Security Agency (NSA). NIAP

will develop tools, test methods and tests for specification-based IT security

products. This means that the security functionality and assurance requirements

fo a product or system must be formally described or specified. These

specifications then form the basis for the development and conduct of tests for

the product or for a class of products (e.g., for a firewall, an access control

device, or even a network router).

6.4. Certification and Management Authorization

The highest level of testing is at the application or system level. At a Federal

agency, this level of testing is certification testing. Certification is the

comprehensive analysis of both the technical and non-technical security controls

and other safeguards of a system. Certification testing establishes the extent to

which a particular system meets the security requirements for its mission and

operational needs. Certification is performed in support of management 's authorization to operate a system. Certification examines the system in the

operational environment and examines external systems that are networked to

the system under test (SUT). One of the major tasks of certification testing is to verify that external systems should not be able to compromise or circumvent the

security features (including cryptographic features) of the SUT. Certification

requires examining not only the technical controls but also all the other security

controls, for example, physical controls, administrative procedures, and

personnel controls. For Federal agencies, it is recommended that certification

testing be performed by a department or organization that is not the developing

organization. This is to ensure independence and objectivity in the testing.

This information was extracted from niap.nist.qov.

61
Implementing Cryptography

Certification testing may be performed against several standards, including the

CC and agency-specific requirements.

At all levels of testing, it is important to be able to trace the implemented

cryptographic controls and other security features through the requirements back

to a standard.

62
Implementing Cryptography

CHAPTER 7

7. SELECTING CRYPTOGRAPHY - THE PROCESS

The process used to select cryptographic methods is similar to the process used

to select any IT method. This selection process is documented in the system

development life cycle model that contains four phases: planning, definition,

acquisition, and operations (including disposal). The system development life cycle model may be embedded in any of the three major system developmental

approaches:

- waterfall - the phases are executed sequentially;

- spiral - the phases are executed sequentially with feedback loops to

previous phases; or

- evolutionary - there is replanning at each phase in the life cycle based on

feedback. Each phase is divided into multiple project cycles with

deliverable measurable results at the completion of each cycle.

The goal of the selection process is to specify and implement cryptographic

methods that address specific agency/organization needs.

Prior to selecting a cryptographic method, an agency should consider the

operational environment, requirements of the application, the types of services

that can be provided by each type of cryptography, and the cryptographic

objectives that must be met when selecting applicable products. Based on the

requirements, several cryptographic methods may be required. Also, both secret

key and public key cryptography may be needed in one system: each performing

different functions.

The following questions should be addressed in determining the appropriate

degree of security, including cryptography, which will be required for a system:

- How critical is the system in meeting the organization's mission?

- What are the security/cryptographic objectives required by the system,

e.g., integrity, confidentiality?

- What regulations and policies are applicable in determining what is to be

protected?

- What are the threats that are applicable in the environment where the

system will be operational?

63
Implementing Cryptography

- Who selects the protection mechanisms that are to be implemented in the

system?

- Are the users knowledgeable about cryptography and how much training

will they receive?

The answers to these questions can be used to formulate a strong

developmental approach to integrating cryptographic methods into existing or new systems. A sound approach in integrating cryptographic methods is to

develop requirements that are derived from the protection goals and policies for

the system. The goals and policies are derived from a risk assessment. The

following areas relate specifically to cryptography and should be included when

developing requirements:

- security of the cryptographic module

- hardware versus software implementation

- applying cryptography in a networked environment

- Implementing Fl PS-validated algorithms

^ - secret key versus public key cryptography

- key management

It is important to be able to demonstrate traceability from the requirements back

to the policies and goals and associated risk assessment.

There are other issues to be addressed in achieving overall security.

Cryptography is best used when it is designed as an integrated part of the

system, rather than as an add-on feature. When this cannot be done,

cryptographic functions should be carefully added so that the security that they

are intended to provide is not compromised. The least effective approach to

implementing cryptography is to immediately begin implementing technical

approaches. (Note: implementing technical solutions without determining the

requirements is never recommended.) Also, cryptographic methods are intended to address specific security risks and threats. Therefore, implementing

only cryptographic methods, and no other security mechanisms in a system, will not necessarily provide adequate security. The example described in section 8.3

(Treasury Electronic Certification System) provides an illustration of selecting and

implementing cryptographic methods. As illustrated by the example, a

cryptographic solution may be initially implemented as a pilot project to ensure

the solution is effective.

By consistently replacing traditional methods, the security and efficiency of a

system improves. Benefits from replacing handwritten signatures with electronic or digital signature techniques include reducing the possibility of forgery,

reducing administrative processing time, and decreasing the burden of

maintaining "traditional" paperwork. A system implementing cryptography will naturally generate new types of documentation, and the cryptographic

64
Implementing Cryptography

technology should be applied in handling that documentation. Security officers,

for example, may have to generate and sign requests for keys or cryptographic

modules. Instead of using paper forms, electronic forms could be generated,

signed, and sent to the appropriate parties, who can verify the signatures and act

on the request in a very timely manner.

Figure 9 illustrates the system development life cycle model phases and the

tasks that are to be performed within each phase when specifying, selecting, and

implementing cryptographic methods. These tasks should be performed when

acquiring and implementing new systems requiring cryptographic products or when acquiring cryptographic products for existing systems. The tasks listed in Figure 9 and discussed in this guideline are tailored to cryptographic methods.

Also, because of the role cryptographic methods play in protecting sensitive

information, greater emphasis should be placed on developing applicable

documentation, (e.g., user procedures and crypto-officer manuals) and

implementing ongoing operational controls, (e.g., key management).

In general, the tasks are listed in sequence; (e.g., identifying potential

countermeasures) is performed prior to executing certification testing.

Realistically, some of the tasks may be executed concurrently, for example,

performing a risk assessment and developing objectives; and selecting and

implementing controls and developing applicable documentation. To ensure that a cryptographic product is correctly implemented to provide appropriate security

functionality, all tasks should be performed, particularly documentation

development, training, and ongoing operations tasks. The phases are described

in more detail in the following sections, with a focus on cryptography.

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7.1. Planning Phase

In the Planning Phase, the goal is to document the objectives that the potential

cryptographic methods/techniques are intended to address. These objectives are partially based on applicable policies and regulations. Objectives are also

derived from the existing (or proposed) security environment and a preliminary

risk analysis with identified threats and vulnerabilities. Policy identification and

development, risk assessment, and objective development tasks are described in the following sections.

7.1.1. Security Policies

According to NIST Special Pub. 800-12, An Introduction to Computer Security:

Ttie NIST l-landbook, computer security policy is defined as the "documentation

of computer security decisions." This includes management's directives to: (1)

create a computer security program, establish its goals, and assign

responsibilities; (2) specify security rules for particular systems, and (3) develop

policies such as an organization's e-mail privacy policy or fax security policy.

After policies are established, requirements (including security and cryptographic

requirements) are specified and an overall system design is developed. The

system design includes software and hardware implementations, procedures,

environmental requirements, physical security considerations, etc.

Typically, policies are based on the need to protect IT resources, data and

information. Security policies exist at all levels of an organization, from agencylevel policy to application specific policy. There are also security policies that are

applicable to all organizations or agencies - these are at the Federal and state

level. Federal-level policies relative to IT security and, more importantly, to the

use of cryptographic techniques give a consistent security direction for the

protection of Federal IT resources. Policies at the Federal level and at the

agency (or organizational) level can be used in making protection decisions at

the application level.

1 . Federal policies provide guidance on using cryptographic techniques, for

example, guidelines for replacing handwritten signatures and agency

responsibilities for protecting information. Federal policies are developed

by Congress and are applicable to all relevant agencies and systems,

{e.g., The Privacy Ac().

2. Agency policies include the mission statements regarding the security

(confidentiality, availability, integrity, non-repudiation) of the application

systems that support the mission. Agency policies set the organizational

strategic directions for security and assign resources for their

implementation. Agency policies may include issue-specific policies that

focus on areas of current relevance or concern to the organization.

67
Implementing Cryptography

Agency policies are typically developed by upper-level management

because they affect the entire agency/organization.

Agency policies directly impact program policy by providing guidance on

what should be included in a program policy. For example, agency policy

on digital signatures may require a specific system to implement a specific

cryptographic method. Also, agency policy on protecting the

confidentiality of certain data records may result in the development of a

confidentiality policy enforced through the implementation of secret key

encryption.

Compliance to an agency policy is critical to the effective selection and

use of security methods. Program policies impact lower level policies and

should be used as a starting point for writing system, program, and

application specific policies. Similar to security requirements, it is important to have traceability Uom the lowest level policy to the highest

level policy - to show how the low-level policies were derived and to

ensure that their specificity accurately reflects the needs of the

organization.

Agency policies may provide the justification for system policy to require

the use of cryptography to replace or supplement conventional security

controls or procedures.

4. Application policies are very specific in setting usage and configuration

guidance for cryptographic controls. These policies consist of security

objectives and operational security rules. These policies are system

specific.

The developers and users of a system typically produce application

policies. Users understand how their systems operate and the goals and

objectives each system addresses. Developers identify security features

that meet a policy and the associated costs for that feature. Application

policies may vary in length from one page to several sections depending

on the sensitivity of the information that needs to be protected and the

number of risks to be mitigated.

Example 1 illustrates a sample policy hierarchy. The Federal policy is the most

general and the application policy is the most specific. This hierarchy illustrates

the traceability of the lowest policy (application) to the highest (Federal).

68
Implementing Cryptography

Example 1. Sample Policy Hierarchy

POLICY TYPE POLICY STATEMENT

Federal Policy Protection of information must be

commensurate with the risk of

unauthorized disclosure.

Agency Policy information that is accessible via the

network will be protected from

disclosure using cryptographic

techniques.

Application Policy On-line access to employment

candidates will be made available to

those in the personnel office and

those managers currently hiring new

employees. Access to candidate

information is available over the

network using the application,

cryptographic software implementing

confidentiality controls, and proper

user authentication.

Policies (and applicable laws and regulations) can be used effectively in the

design, development and implementation of cryptography-based controls and

procedures, if they are implemented in a practical (real-world) manner.

The next major task in the planning phase is to perform a risk assessment and,

specifically, identify the unique requirements associated with each IT system.

After the risk assessment has been performed, policies should be developed

regarding the use of evaluated operating systems and validated cryptographic

modules in a range of environments. Also, policies that have been previously

written may need to be revised or tailored throughout the system life cycle.

The following are some topics that should be addressed when developing

cryptography policies and requirements:

1 . Policies regarding algorithm usage and algorithm parameter

configuration,

2. Policies regarding the classes of users (e.g., crypto-officers, networked

users, operators) that may use the cryptographic methods and

assigning associated privileges,

3. Identification and authentication requirements when a user first accesses a system or cryptographic module,

69
Implementing Cryptography

4. Procedures employed when adding, modifying, or deleting users and

user privileges associated with cryptographic methods/products,

5. Policies defining when confidentiality controls, integrity controls, and

advanced authentication techniques are required,

6. Security measures relating to the physical environment of a

cryptographic method/product,

7. Audit procedures,

8. Guidelines for requiring non-repudiation,

9. Guidelines for performing risk assessments to:

- Ensure the unique risks of an IT system are considered,

- Evaluate the potential risks and determine the level of control

required to minimize the risks, commensurate with the cost or value of

the data,

10. Key Management including key distribution, generation, use,

destruction, and archiving.

1 1 . Backward compatibility of software/hardware and architecture.

12. FoHA/ard compatibility with envisioned future developments such as

new cryptographic techniques, digital signature systems,

authentication mechanisms, FIPS PUBs, and

13. Interoperability between governments, commercial communities, law

enforcement communities, etc.

Example 2 lists sample policy statements that are applicable to a Public Key

Infrastructure (PKI) Policy Certification Authority (PCA) application. Because the

policies are for a specific application and technology, they are at a low level of

detail.

70
Impiementing Cryptography

Example 2. Application Policy Statements

- Identification and Authentication (l&A) Requirements: When a user registers

his or her certificate, the user must provide required l&A information to the

certificate issuer to prove that he/she is indeed the claimed person.

- Security Controls: Each PCA must specify the security measures that it will employ for (1) the hardware and software that are used for certificate

generation and signing and (2) maintaining certificate revocation lists (CRLs).

- Audit Procedures: Each PCA must specify the procedures for manual audits.

The procedures may include a schedule of the manual audit and may also

include provisions for impromptu audits.

7.1.2. Risk Assessment

Risl< management cons\s\s of two components:

- Assessing risks using a risk-based approach to determine the impact of

given losses and the probability that these losses will occur. The major

losses addressed by cryptographic methods are the unauthorized disclosure

and modification of data.

- Selection and implementation of countermeasures that either reduce the

probability of threat occurrence or minimize the impact of loss. The goal is to reduce the risk to an acceptable level.

The purpose of an IT risk management process is to ensure that the impacts of

threats are known and that cost-effective countermeasures are applied to determine adequate security for a system. Adequate security \s defined in 0MB

Circular A-130, Appendix 111, as "security commensurate with the risk and

magnitude of harm resulting from the loss, misuse, or unauthorized access to or

modification of information. This includes assuring that systems and applications

used by an agency operate effectively and provide appropriate confidentiality,

integrity, and availability through the use of cost-effective management,

personnel, operational, and technical controls." This definition explicitly

emphasizes the risk-based policy for cost-effective security established by the

Computer Security Act.^^

R/s/c assessment, the process of analyzing and interpreting risk, includes the

following activities.

The Appendix no longer requires the preparation of formal risk analyses.

Rather than continue to try to precisely measure risk, security efforts are better

served by generally assessing risks and taking actions to manage them.

71
Implementing Cryptography

- Identify assets

- Assess current security and protection mechanisms

- Identify and classify threats affecting:

- Integrity

- Confidentiality

- Authentication

- Non-repudiation

- Availability

- Identify potential losses

- Classify potential losses by criticality and sensitivity

- Quantify cost of loss

- Develop risk scenarios

- Develop risk measurement levels

- Identify potential countermeasures/safeguards

- Evaluate potential countermeasures so that implementation decisions

can be made

- Perform cost/benefit analysis for proposed countermeasures. (The

analysis should include both monetary and non-monetary

perspectives.)

- Risk mitigation involves the selection and implementation of security controls

to reduce risk to an acceptable level. In Federal agencies, the common

method to select security controls (including cryptographic methods) is to

develop a Request for Proposal (RFP) and select the proposal that provides

the best solution.

The following two examples illustrate how cryptographic methods can address

integrity and non-repudiation threats.

72
Implementing Cryptography

Example 3. Threat Mitigation

Security Control to Mitigate Threat to Integrity: Both secret key and public

key cryptography can be used to ensure integrity. When secret key cryptography

is used, a data authentication code (DAC)^^ is generated. Typically, a DAC is stored or transmitted with the data. When the integrity of the data is to be

verified, the DAC is generated on the current data and compared with the

previously generated DAC. If the two values are equal, the integrity (i.e.,

authenticity) of the data is verified.

Public key cryptography verifies integrity by using public key signatures and

secure hashes. A secure hash algorithm is used to create a message digest

(hash). The hash will change if the message is modified. The hash is then

signed with a private key. The hash may be stored or transmitted with the data.

When the integrity of the data is to be verified, the hash is recalculated and the

corresponding public key is used to verify the integrity of the message.

Security Control to Mitigate Threat to Non-repudiation: Data is electronically

signed by applying the originator's private key to the data. The resulting digital

signature can be stored or transmitted with the data. Any party using the public

key of the signer can verify the signature. If the signature is verified, then the

verifier has confidence that the data was not modified after being signed and that

the owner of the public key was the signer. A certificate binds the public key to

the identity of the signer.

Typically, a risk assessment is performed for all new and existing systems, even

if it is not called a formal risk assessment. The type of risk assessment that is performed is usually a qualitative analysis, rather than a formal quantitative

analysis and the results are used in developing the system requirements and

specifications. A team comprised of users, system developers, and security

specialists typically conducts the risk assessment. The scope of this task varies

depending on the sensitivity of the information and number and types of risks that

need to be addressed. For systems with minimal security requirements, the risk

assessment may be a few pages in length.

7.1.3. Security Objectives

The third major task in the planning phase, in addition to specifying policies and

performing a risk assessment, is to develop security objectives. These

objectives are at a high level and should address security, in general, and

cryptography, in specific. Example 4 lists sample security objectives.

A DAC is commonly referred to as a Message Authentication Code (MAC).

73
Implementing Cryptography

Example 4. Security Objectives

1 . Security mechanisms should be able to evolve as technology evolves.

2. Integrity. The correctness of cryptographic keys and other critical security

parameters must be preserved. Authentication, authorization and nonrepudiation should be supported. The correctness of the security

mechanisms/features should be ensured.

3. Availability. The security mechanisms/features should be continually

available (at least 99.5% of the time). Availability periods must be tailored

to particular systems or environments. Response time to suspected

compromise, for example, disclosure or modification, should be

minimized. Systems should be responsive and adaptable to changing

security requirements and threats.

4. Assurance: An acceptable level of assurance should be maintained to

ensure that the security mechanisms/features are operating correctly.

There should be no increase in vulnerability to an individual system due to

a connection to external systems or networks, e.g., the Internet. A risk

assessment should be performed prior to linking a system to an external

system to determine the level of risk.

5. Authentication: The security mechanisms/features must provide at least

the same level of accountability as paper-based systems. Accountability

is typically accomplished by identifying and authenticating users of the

system and subsequently tracing their actions. User accountability should

be limited to security-relevant conditions. Accounting data should be

accessible to designated crypto-officers and operators. Accountability

should be reflected in an audit trail.

6. Digital signatures: Digital signature techniques may be used to validate

the:

- identity of the signer of a message and

- integrity of the information received from the signer of that

information.

Digital signatures may represent an individual or an entity (system).

7.2. Definition Phase

In the Definition Phase, the objective is to develop the

requirements/specifications for the proposed cryptographic methods. After the

requirements have been developed, general selection criteria based on these

requirements are produced. Finally, categories of methods that meet the

requirements are identified. The security requirements are based on user needs

and estimates of an organization's resources to meet proposed requirements.

74
Implementing Cryptography

Requirements sliould be detailed - this aids in product selection, implementation,

and testing.

7.2.1. Security Requirements/Specifications

The cryptographic requirements may be divided into three categories: functional,

assurance, and environmental requirements. (The following definitions are taken

from the CC.)

Functional requirements describe the expected security behavior of a

product/system and are intended to meet the security objectives.

Assurance requirennents ensure that an IT product or system meets its security

objectives. Assurance that the security objectives are achieved by the selected

security functions is based on the following two factors:

a) confidence in the correctness of the implementation of the security

functions, i.e., the assessment whether they are correctly implemented;

and

b) confidence in the effectiveness of the security functions, i.e., the

assessment whether they actually satisfy the stated security objectives.

Environmental requirements are intended to counter threats and risks in the

operating environment of the product/system and/or cover any identified

organizational security policies and assumptions. Environmental requirements

generally apply to the system, rather than to specific cryptographic methods.

Environmental requirements address the physical and operational controls that are applicable to the system.

Environmental requirements are one component of the security environment.

The security environment includes all the laws, organizational security policies,

customs, expertise and knowledge that are determined to be relevant. The

security environment also includes the threats to security that are present in the

physical environment.

Table 3 identifies security objectives and requirements for cryptographic

components that may be addressed by cryptographic methods and techniques.

The purpose of the table is to provide individuals with a roadmap to identifying

cryptographic functional and assurance requirements in the CC classes that will meet the needs of a system in an organization. After the functional and

assurance classes are selected, the specific requirements are extracted from the

CC. The specific requirements may need to be refined/tailored to meet security

objectives. The tailoring operations are defined in the CC. Table 3 is not

intended to list all the specific CC requirements; rather it serves as a reference

guide to the CC classes. To effectively use the table, it is important to have

75
Implementing Cryptography

documented the objectives that must be addressed. These objectives were

developed in tasks in the Planning Phase.

- Column 1, Cryptographic Category, covers the areas related to the design

and implementation of a cryptographic product/module. Some examples are

roles and services, physical security, and cryptographic key management.

- Column 2, Security Objectives, lists the security objectives applicable to a

cryptographic category.

- Columns 3 and 4, Functional and Assurance Requirements, list the

functional and assurance requirements that address the security objectives

for a cryptographic category. The functional and assurance requirements

are listed by CC class, for example, audit, cryptographic support,

identification and authentication, configuration management, guidance

documents, development.

- Column 5 contains Procurement Recommendations to ensure the

cryptographic requirements are adequately addressed.

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82
Implementing Cryptography

7.2.2. Cryptographic Method Example

The following example focuses on a specific cryptographic method, digital

signatures, and illustrates how requirements may be derived from a high-level

digital signature policy statement.

Example 5. Digital Signature Policy

Background: Historically, handwritten signatures were used to provide

authenticity and liability for a document. The proposed successor to handwritten

signatures is digital signatures.

Policy Statement. Digital signatures will be accepted as valid only if the user who

verifies a signature has an acceptable level of assurance of the integrity of the

electronic document that was signed and the identity of the signer of that

document. In addition, the verifier must be able to trust that the signer will be

held legally responsible for the information content of the document.

One of the digital signature policies is to ensure the integrity of electronic

documents and provide non-repudiation of document origin. The requirements

resulting from this policy include all three types: functional, assurance and

environmental.

Example 6. Digital Signature Requirements

Requirements:

1 . Document preservation. Associated signatures and the certificates necessary

to verify those signatures must accompany electronic documents. A record of

certificate validity must also be kept along with an audit trail of document

movement. Expert testimony about this entire procedure and the audit data

collected will lay the foundation for the testimony if documents are required as

evidence.

2. Digital signatures do not, by themselves, provide time-related information. A

trusted time stamp is required to prove when a document was originated or received. This service must be provided by a trusted third party, which may be

serving the purpose of a notary. The originator will generate a hash of the

document and send a copy of the document and the hash to a private sector

vendor serving as a notary. This trusted party could time and date stamp the

hash of the document, store a copy of the hash and the document, keep an audit

log of the action, and serve as an intermediary between the document's

originator and receiver.

83
Implementing Cryptography

3. Establishment of user and CA responsibility. The document signer must be

responsible for protecting the private key used to sign a document and obtaining

time stamped document receipts, when required. A document verifier must

ensure that all certificates used to verify a received document are valid at the

time the document is received, the received document is time stamped, and the

required information is archived in case of litigation. The CA is responsible for

protecting the private key used to sign certificates, establishing the identity of its subscribers, and providing certificates and revocation information in a timely

manner.

4. Each entity, whether an originating or sending entity or a CA, must maintain

an audit log of digital signature related activity, including messages sent and

received, activity by persons associated with the signature process and other

security-relevant events.

5. Policies and procedures must be established to ensure that control is maintained on all processes involving the electronic authorization and

authentication of electronic documents.

6. Policies and procedures must be established that will ensure that an

approved process protects the distribution and communication of authorities.

7.2.3. Selecting Cryptographic Countermeasures

The final task in the definition phase is to identify categories of cryptographic

methods/techniques that meet the requirements and mitigate the specific risks.

(Note: there may be more than one method category that can mitigate each risk.

For example, both DES and digital signatures can protect against the undetected

modification of data.) For many of the methods, there are assurance features

that increase the confidence that the method performs correctly.

Table 4 lists the technical and assurance features that meet the technical and

assurance requirements documented in Table 3. The features in Table 4 map

directly to the requirements listed in Table 3.

- Column 1 lists the Cryptographic Category.

- Column 2 identifies the risks and attacks that apply to a cryptographic

category, for example, unauthorized access or unauthorized disclosure.

- Columns 3 and 4 list the technical and assurance features that are

applicable to a cryptographic category and mitigate the potential risks.

Where applicable, the technical and assurance features are numbered and

listed in ascending order of protection, to address increasing levels of risk.

84
Implementing Cryptography

The levels vary from 1 to 4, corresponding to the security levels in FIPS PUB

140-1.

- Column 5 lists the FIPS PUBs that describe the technical features. The

information included in the cryptographic category columns is the same as

that presented in the requirements table (Table 3). This provides for

traceability from the requirements to the methods and features.

Tables 3 and 4 illustrate traversing from a high level of abstraction in the

requirements to a lower level of granularity in identifying specific features. It is important to understand that Table 4 does not specify the necessary conditions

for the secure implementation of a product in a particular system/application.

This task is left to those who implement the system.

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93
Implementing Cryptography

To clarify how all this information fits together, Example 7 walks through the two

tables and illustrates the process of defining requirements, identifying risks, and

then selecting cryptographic methods that meet those requirements and

mitigates the risks. Additional explanatory information is included in brackets.

Example 7. Using Tables 3 and 4

- Risk/Attack: Unauthorized disclosure of data or undetected modification of

data (intentional and accidental) during transmission or while in storage [the

risk was identified as the result of a risk assessment]

- Functional Requirements: Implement FlPS-approved security methods for

data integrity assurance [the requirement addresses the risk]

- Assurance Requirements: Tests [the cryptographic algorithm must be tested

to ensure that it is compliant with the FIPS standard. Also, tests may be

executed to ensure the algorithm was implemented correctly.]

- Cryptograptiic Category/Services: Cryptographic algorithms [these methods

provide features that track any change, e.g., modification, insertion, deletion,

to security-relevant data]

- Technical Features: FlPS-approved DES algorithm [implementations of the

algorithm which have been tested and validated by NIST are compliant with

the standard]

- Assurance Features: NIST conformance tests [the tests are used to validate

compliance with the standard]

- Cryptographic Toolkit Reference: FIPS PUB 46-3: DES [specific DES

modes can be used to calculate a data authentication code that provides for

data integrity]

- Procurement Recommendations: Federal agencies that use cryptography to

protect sensitive information must use systems that have been FIPS PUB

140-1 validated.

7.3. Acquisition Phase

During the Acquisition Phase, one product/module is selected that meets the

documented requirements. The product is then configured, implemented, and

tested in the system. There are several types of testing that may be required,

such as validation against FIPS PUB 140-1, system testing, and certification

testing in support of system management authorization. Extensive testing of

cryptographic controls is particularly important because of their role in ensuring

the security of the overall system.

94
Implementing Cryptography

A second major task in the Acquisition Phase is to develop documentation for users and cryptographic officers to inform them of their responsibilities in maintaining a secure system. The Department of Energy project described in section 8.1.1 identifies some acquisition issues.

The next two sections specify some tips for implementing cryptography.

7.3.1. Implementation Approach

The security provided by a cryptographic system depends on the mathematical

soundness of the algorithm, the length of the cryptographic keys, key

management, and mode of operation. A weakness in any one of these

components may result in a weakness or compromise to the security of the

cryptographic system. A weakness may be introduced at any phase of the

system life cycle.

During product design and development, it is the responsibility of the

manufacturer of a cryptographic product to build a module that meets specified

security requirements and conforms to a FIPS. However, conformance to a

standard does NOT guarantee that a particular product is secure. To provide a

level of assurance that the cryptographic product is secure, the product should

be validated in the CMVP. The level of security in a cryptographic

product/module must also be considered in the product selection phase. During

this phase:

- Identify information resources and determine the sensitivity to and

potential impact of losses. Determine security requirements based on risk

assessment and applicable organizational security policies. Look at data

sensitivity and the environment in which the data is placed. Consider

threats to the data or application as a whole, and what level of risk is acceptable.

- Determine the acceptable safeguards for the system. Determine which

cryptographic services provide an acceptable safeguard. Define those

security features that are desirable for use and determine the appropriate

security level from FIPS 140-1.

Finally, it is the responsibility of the integrator to configure and maintain the

cryptographic module to ensure its secure operation because the use of a

cryptographic product that conforms to a standard in an overall system does not

guarantee the security of the cryptographic module or of the overall system. To

summarize, the proper functioning of cryptography requires the secure design,

implementation, and use of a validated cryptographic module.

There are many interdependencies among cryptography and other security

controls, for example:

95
Implementing Cryptography

- Physical Access Control. Physical protection of a cryptographic module is required to prevent, or detect, physical replacement or modification of the

cryptographic system and the keys within the system.

- Logical Access Control. Cryptographic modules may be embedded within

a host system. With an embedded module, the hardware, operating

system, and cryptographic software may be included within the

cryptographic module boundary. Logical access control may provide a

means of isolating the cryptographic software.

- User Authentication. Cryptographic authentication techniques may be

used to provide stronger authentication of users. (Advanced

authentication techniques are discussed in a later section.)

- Assurance. Assurance that a cryptographic module is properly and

securely implemented is essential. NIST CMVP provides assurance that a

module meets stated standards.

- Integrity Controls. Cryptography may provide methods that protect

security-relevant software, including audit trails, from undetected

modification.

The major rule is: BUYER BEWARE!! Example 8 illustrates how important it is to correctly implement and manage all of the security and cryptography controls

to ensure that keys are not compromised.

Example 8. Implementation Problems

- Cryptographic algorithm may be strong, but the random number generator

(RNG) may be weak

- RNG may be strong but the Key Management weak

- Key Management may be strong but the user authentication weak

- Authentication may be strong but the physical security weak

The following three rules guide the implementation of cryptography.

- Determine what information must be protected using a cryptographic function.

The implementor should be aware of the information that is being signed and

encrypted. Fields containing sensitive data should be identified, and then a

determination should be made of what cryptographic functions should be applied

to those fields: integrity, authenticity, and/or confidentiality.

96
Implementing Cryptography

- Protect data prior to signature generation/verification and

encryption/decryption. Be careful of fiow data is tiandled during tiiese

processes!

Implementers should be very careful about how data is handled before it is signed/verified (encrypted/decrypted). If data is stored in a central database and

transferred to the computer only at the time the cryptographic function is performed, the data should be very carefully protected during transmission. If data is not carefully protected, an intruder could potentially alter data before a

signature is generated, without the signer's knowledge. The data should be

signed on the signer's machine, not in the central database.

- Provide thie capability for users to locally view all data that is being

signed/encrypted.

Users should be able to see all the data that is being signed, and it should be

clearly marked for the signer. Also, users should know what is encrypted. It is not essential that all data being signed/encrypted should appear on one screen,

but the user should at least be able to view all of the data before performing the

cryptographic function.

7.4. Operations Phase

In the Operations Phase, the goal is to ensure the continued secure operation of

the cryptographic methods. Two critical areas are training and the management

of cryptographic components.

7.4.1. Training and Documentation

It is particularly important that all users be aware of their responsibilities, the

procedures they must follow in ordinary as well as unusual circumstances, and

who they should contact for assistance. These procedures should be standard

among all sites in the system. Of special importance are the central sites, where

security officers are responsible for equipment that might generate and manage

keys for system users. If no documented set of procedures is followed,

weaknesses may be introduced into the system such as transmitting data in clear

text.

7.4.2. Life Cycle Management of Cryptographic Components

Maintenance of cryptographic components is critical to ensure the secure

operation and availability of the module/product. For example, cryptographic

keys that are never changed, even when disgruntled employees leave, are not secure. The following are maintenance areas that need to be considered during

the cryptographic product life cycle:

97
Implementing Cryptography

1 . Hardware/firmware (e.g., new capabilities, expansion of the system to

accommodate more users, replacement of non-functional equipment,

change of platforms, hardware component upgrades, etc.)

2. Software maintenance/update (e.g., new capabilities, fixing errors, improved performance, key replacement, etc.)

3. Application maintenance (e.g., changes in roles and responsibilities,

remote updates, updating passwords, deleting users from access lists,

etc.)

4. Key maintenance (e.g., key archiving, key destruction, key change, etc.)

5. Maintenance personnel. Who is allowed to perform maintenance? Do

maintenance personnel require clearances, or do authorized users monitor maintenance activities? What must be removed from the system

prior to maintenance? How is the correctness of the maintenance

procedure ascertained?

Configuration management (CM) is needed for areas 1 and 2. CM ensures the

management of system and security features through the control of changes

made to a system's hardware, firmware, software, and documentation. The

documentation may include user guidance, tests, test scripts and test

documentation.

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Implementing Cryptography

CHAPTERS

8. PUTTING IT ALL TOGETHER - EXAMPLES

Included in this chapter are a few examples of projects that use cryptography.

These projects illustrate how cryptography is used in the Federal government. In general, the projects have involved upgrading existing systems, while adding

additional security and cryptographic capabilities. New systems that are being

proposed and designed for Federal agencies focus on the PKI architecture and

include digital signature, authentication, and encryption capabilities.

The descriptions in this chapter provide an overview of the projects and are not

intended to include extensive detail. If more information is desired, contact the

applicable agency.

8.1. Key Recovery Demonstration Project (KRDP)'''*

In May 1996, 0MB released a white paper titled Enabling Privacy, Commerce,

Security, and Public Safety in the Global Information Infrastructure. This paper

stated that, "government and industry must work together to create a security

management infrastructure and attendant products that incorporate robust

cryptography without undermining national security and public safety." In support

of this goal, a Key Recovery Demonstration Project (KRDP) was initiated in order

to demonstrate the practicability of the recovery of keys that support data

encryption in Federal government applications. Approximately ten Federal

agencies participated in the pilot program in which different key recovery

technologies were implemented, tested, and evaluated. Following are

descriptions of two of these projects.

8.1.1. Department of Energy: EZ_ERA32 and the KRDP'*^

The KRDP seeks to test key recovery as part of a security component of an

electronic commerce initiative with grantee organizations. This initiative has

been underway since 1992, when a feasibility study conducted by Federal

Information Exchange (now doing business as RAMS) found that grantee

institutions were willing to migrate toward electronic research administration.

Based on the findings, the Department of Energy (DOE) awarded a cooperative

agreement to RAMS in 1994 to work on the NewERA project with research

institutions and Federal funding agencies to demonstrate electronic research

administration across the Internet and to provide "one face to government."

Electronic research administration has a number of important benefits including:

KRDP information may be found at the web site: www.qits-sec.treas.qov. '^^ The information in this section was extracted from a report prepared by the

Department of Energy.

99
Implementing Cryptography

- More efficient and timely proposal submissions;

- Improved data management capabilities;

- Integrated data functions among related operations;

- Reduced rekeying of data and administrative time; and

- Substantial paper savings.

Research applications may contain sensitive data, may involve considerable

amounts of money, and can contain valuable intellectual property. Therefore,

investigators are very concerned about the security of electronic transmissions.

Failure to address security will inhibit widespread adoption of Electronic

Research Administration and EDI. The requirements for cryptography include:

• Confidentiality: A confidentiality service to prevent the disclosure of

information to unauthorized parties by means of strong encryption.

• Inteqritv: Providing cryptographic based integrity by means of message

hashing to prevent undetected and unauthorized modifications of the

information.

• Authentication and Non-repudiation : A user authentication service to provide

verification of the sending identity by means of digital signature and the use of

signature certificates.

• Kev Recovery: Providing a means of retrieving a session key for the purposes

of re-acquiring plaintext information from the ciphertext files in the event that

the original decrypting key is no longer available.

The KRDP Pilot Project has provided the means to test the capability of

emerging security technologies to meet the security requirements of electronic

data interchange (EDI) over the Internet that is the heart of NewERA.

One benefit of the KRDP that has already been realized is the development of

EZ_ERA32, a prototype security product by RAMS. In the absence of a

commercial product that provided the complete set of security functionality,

EZ_ERA32 was developed to tie together the different commercially available

components. RAMS was responsible for seamlessly integrating the services and

software of the vendor partners into the prototype software. EZ_ERA32 allowed

the extraction of grant application data from user productivity tools such as

Microsoft Excel and Word. The extracted data was then processed to generate a

standard transaction set that was encrypted.

The software also provided functionality for public-private signature keys, publicprivate exchange keys, and Certificate Signing Request generation as well as

other configuration utilities (email configuration, establishment of trading partner

relationships and exchange key storage, etc.) that allowed the exchange of

100
Implementing Cryptography

secure EDI transactions to occur.

Partnering Vendors of Commercial Software and Services: Wherever possible,

COTS products and sen/ices were utilized for the ERA project. The participating

companies cooperated to provide the various security elements as described

below.

Certificate Authority (CA): VeriSign provided CA services. A Web

interface developed by VeriSign provided a site into which a user would

paste a CSR generated by the EZ_ERA32 software. An EDI Certificate

containing the public signature key was signed using the RSA algorithm

and returned to the trading partner as a standard PKCS-7 file where it was

stored by the EZ_ERA32 application. This certificate was then included

within the encrypted package and sent to a recipient so the recipient could

verify the identity of the sender and the integrity of the received EDI

transaction

Key Recovery Agent (KRA) : Requests for plaintext retrieval, whether from

individual registered users or authorized law enforcement officials, must

satisfy the procedures and rules of the designated KRA before a retrieval

can be accomplished. Only authorized personnel can request a file recovery. All communications between the client and the Key Recovery

Center (KRC) are encrypted. The KRC does not store (escrow) session

keys, user keys, or user message files. Only an encrypted session key is returned to the client software where it is used to retrieve the plaintext

data.

TIS Labs CrvptALLProduct: CryptALL provides interfaces, dynamic link

libraries, utilities, and sample code which can be utilized by application

software to integrate the encryption and recovery capability into their

products. The Client software runs on the application machine and also

provides an interface for configuration and registration with a KRC. The

software includes the cryptographic service provider module used for key

generation and by the encryption/decryption processes of application

software.

The System Architecture diagram in Figure 10 illustrates the relationship of

EZ ERA32 and the COTS services and software.

101
Implementing Cryptography

Certificate

Autliority

OAriSign)

Key Recovery

Center (SourceKey)

Figure 1 0. System Architecture

Findings:

Implementation of security functionality requires a whole new software

setup and configuration. Many pieces must be set up (key generation,

exchange partner agreements, obtaining a certificate, registration with a

KRA, etc.) to create a complete environment. A basic understanding of

how each of the security features works is necessary to get a system

operational.

Participants indicated that they found the installation and configuration

moderately difficult to perform. Since the system must be maintained over

time, basic training for operations personnel is highly desirable. Educated

and qualified support for operations personnel who must perform these

tasks is critical.

It takes time to install and set up security features since a number of

different features must be configured (e.g., keys, certificates, trading

partner relationships, key recovery center certificate and accounts).

Operations personnel must be provided with sufficient time to perform

these tasks.

102
Implementing Cryptography

4. Interoperability problems still remain.

5. Once installed and correctly configured, the security functionality was fairly

invisible to the end-users. Encrypted messages were successfully sent

and acknowledgments received. If the KRC was available, those who

attempted to perform recoveries were able to do so.

8.1.2. U.S. Electronic Grants'*^

The U. S. Department of Transportation (DOT) developed the U.S. Electronic

Grants System (USEGS). The production system, currently being tested, will permit grant customers to exchange required data and files with Federal agency

databases (Extranet) through data screens running in a Web browser. To

facilitate KRDP testing, DOT designed a special version of the grants system

called the Secure Electronic Grants System (Secure EGS). The project involved

developing a security approach and technology, extensive testing, evaluating the

results, and identifying remaining tasks.

System security features were developed to provide authentication,

confidentiality, integrity, non-repudiation and key recovery. These features were

provided through a PKI based on digital certificates that bound users to their

public and private keys. The keys were used to enable digital signature and

encryption capabilities based on the RSA algorithm. The certificates and keys

were stored on smartcards. Certificates were issued by a contracted CA and

managed using a Lightweight Directory Access Protocol (LDAP) server.

Test and Results: DOT and its partners successfully tested signing, encrypting,

validating, and decrypting grant documents sent over the Internet. These

functions were tested through a Java user interface. Simulated recovery of lost

data ("key recovery") was also tested and demonstrated live at the KRDP

conference in November 1997. These tests also highlighted areas for

improvement including easier user system set-up, a friendlier interface, improved

CA interoperability, a comprehensive registration interface, and more specific

policies and procedures.

Remaining Tasl<s: The KRDP test proved that the technology currently available

for securing electronic grant transactions across the Internet works as

anticipated. However, the test also indicated that significant policy, procedural,

technical, and operational issues must be resolved before a Secure EGS based

on PKI can be implemented. The areas which need to be addressed include

security hardware and software set-up for users, the signing/encryption interface,

the registration process and interface, CA interoperability and cross-certification,

and security policy and procedures.

The information in this section was extracted from a report prepared by the

Department of Transportation.

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Implementing Cryptography

Accomplishments: The KRDP project successfully demonstrated the capability to

conduct secure electronic grant transactions over the Internet through a Java

applet running in a Web browser. Key technology accomplishments include the

following:

Information Broker Based Secure Sockets Layer (SSL) - developed and

implemented SSL in an Information Broker system. SSL provides

presentation layer confidentiality for all objects (data, documents,

spreadsheets, etc.) and transactions. Information Broker middleware

provides object communications services including routing, queuing and

filtering.

SSL Client Authentication - developed SSL client authentication capabilities.

Access to system objects (Information Broker events) is controlled by the

identity and attributes contained in a digital certificate. This approach

requires several enhancements before it can be fully implemented.

Client Authentication - implemented client authentication using ID/password.

PKI - tested and demonstrated application layer PKI (digital signature and

encryption) technology using RSA to encrypt a DES session key. Encryption

provides confidentiality for sensitive grant objects with access limited to

selected recipients. Digital signature provides authentication, object integrity,

and non-repudiation.

Multiple Certificate Directories - tested and demonstrated access to multiple

LDAP directories using Secure EGS so that Federal agency and customer

certificates could be used in transactions.

Tokens - tested and demonstrated PKI using tokens (DataKey smartcards

and readers).

Java - developed, tested and demonstrated the first Java applet/smartcard

interface.

Secure Object Transfer - tested and demonstrated the secure transfer of

objects between clients and a Federal database. This capability enables

grant customers to select files from their PC's file system, send them to the

Federal database, and retrieve them from that database for review and

modification.

User Interface - developed and tested a graphical user interface (GUI)

designed to enable users to conduct secure object transfer activities along

with digital signature and encryption functions.

Key Recovery (KR )

- tested and demonstrated KR using key encapsulation.

This approach streamlines the KR business process by eliminating the need

for key administration and escrow. KRDP Test Results: In addition to developing and demonstrating technology

capabilities, the project involved testing the capabilities with grant customers

104
Implementing Cryptography

(States of Washington and Utah, Cornell University) and other Federal agencies

(the National Technical Information Service (NTIS), NIST). The results indicate

that the technology works as anticipated in a live transaction environment. The

tests identified the following issues:

Organizational Registration - DOT established trading partner and trust relationships during the test with its customers through informal site visits.

These relationships enabled DOT to trust the certificates issued by the

customer's CA. However, an approach based on informal site visits is not

feasible for widespread system implementation.

Individual Registration/Access Control - individual registration was also an

informal process conducted by each customer organization. Based on phone

conversations, certificates were provided to test participants by the Federal

CA or a state designated CA (in Utah). System access rights were provided

by DOT based on phone conversations and personal knowledge of the

customers. Again, these approaches to registration and assigning access

control are not feasible for widespread system implementation.

PKI Authentication/Single Sign-on - ID and password authentication cannot

provide adequate security or single sign-on capabilities. PKI/SSL client

authentication capabilities were developed during the project to provide

strong authentication and single sign-on features. However, significant work

needs to be done to implement and test these capabilities.

Key Recovery - the tested approach to "key recovery" involved the DOT KRA

(NTIS) decrypting objects and providing the clear text back to DOT.

Unfortunately, this approach permitted the KRA access to confidential agency

information. In practice, the KRA should only decrypt the session key

wrapper and pass the object back to the Federal agency for recovery of clear

text. Key Recovery Procedures - as with registration, the process used to request,

authorize and recover information was based on informal relationships, and

lacked specific procedures. This approach is inadequate for a secure KR

operation.

Technology Implementation - although the technology worked well when

implemented in Federal test systems, several issues arose when it was

implemented at customer sites. Most of these issues are related to the

immaturity of the technology, but they must be resolved for the system to be

successful.

Remaining Tasks: The following tasks need to be completed in order to provide a

truly Secure U.S. EGS based on PKI technology:

Organizational Registration - registration, including the establishment of

trading partner and trust agreements, must be defined and tested.

105
Implementing Cryptography

Individual Registration/Access Control- individual registration and assignment

of access control rights will involve electronic interaction between users and

their CAs and Federal agencies. User registration policies and procedures

must be defined and tested.

PKI Authentication/Single Sign-on - Significant work remains to be done to

integrate and test the smartcard and SSL interface. This work is necessary to

provide PKI authentication and single sign-on.

User Interface - a new GUI interface for object management, digital signature

and encryption must be designed, developed and tested.

CA Interoperability - interoperability standards must be defined (most likely by

an industry or standards group) and tested. Federal agencies should only

procure and establish electronic trading partner agreements with compliant

CAs and customer organizations.

Multiple Step KR - this approach to key recovery must be developed and

tested. The multiple step approach will limit KRA access to the session key

wrapper and not permit access to confidential agency information.

KR Procedures - KR procedures, including the multiple step approach, must

be defined, documented, automated and tested.

Customer Testing - as we discovered in the KRDP project, testing by vendors

and Federal agencies is necessary but not sufficient. Extensive customer

testing, revision of system components, and further testing is necessary to

ensure a successful implementation of the Secure U.S. EGS.

8.2. Army Corps of Engineers

The Army Corps of Engineers has implemented electronic signatures in the

Corps of Engineers Financial Management System (CEFMS). CEFMS is a

Corps-wide computerized system that uses databases to manage financial data.

CEFMS migrates numerous financial applications - including purchase requests,

obligations, disbursements, and travel order certification to a completely

electronic format. Corps employees can generate unique electronic signatures

on electronic forms, and other CEFMS users can electronically verify the

correctness of those signatures, eliminating the need to generate paper-based

forms with handwritten signatures. The electronic signature must have all of the

following attributes:

- Unique to the signer,

- Verifiable by a third party,

- Under the sole control of the signer, and

- Linked to the signed data in such a manner that if the data is changed, the

signature is invalidated.

The subsystem of CEFMS that provides this signature generation and verification

capability is the Electronic Signature System (ESS). The ESS uses the DES

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algorithm and key notarization techniques developed by NIST. The ESS was

designed to be a modular system that could be plugged into various applications.

The ESS design is based on cryptography and is designed to implement split

knowledge and dual control. Every user of the ESS must have a unique

cryptographic key stored in a secure mode. The ESS allows for key

management and token initialization, signature generation and verification, key

translation, and message encryption and decryption. Key management and

token initialization are functions of a Key Management Facility (KMF). Messages

are signed and verified using MACs. Key translation, which allows one user to

verify another's electronic signature, occurs at a Key Translation Center (KTC).

In the second phase, a software reference implementation was developed. This

phase involved testing the cryptographic PC adapter used in the ESS. The

cryptomodule incorporates the cryptographic service calls (CSCs) and

application cryptographic commands (ACCs) used to perform the ESS functions.

Testing was performed on the implementation of the ACCs and CSCs to ensure

that they were implemented correctly. Testing was executed before the ESS

went operational. By finding some cryptographic bugs in the adapter before

thousands were distributed to ESS users, the dissemination of weak

cryptography that could have led to incorrect signatures was prevented.

8.2.1. ESS Architecture

In general, the ESS has two sites that each contains a user key database, which

mirrors the other site's database and software, that acts as a central KMF/central

KTC (cKMF/cKTC*^). A backup computer is stored in the immediate vicinity of

the primary KTC machine, along with several cryptomodules that can be used if those in the primary computer fail. Figure 1 1 illustrated the ESS design.

This will be referred to as the KTC, since both functions are centrally provided

on a single machine at each KTC site.

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Figure 11. ESS Architecture

Both KTCs maintain a complete user key database containing keys for all valid users of the ESS. Central Security Officers are responsible for using the KTC

software to initialize tokens for all users of the ESS. Each KTC remains activated

twenty-four hours a day, seven days a week.

The ESS has multiple user sites, which are connected to one of the main

processing centers via the CEFMS Wide Area Network (WAN), depending on

their location. District Security Officers (dSOs), Security Administrators (SAs),

and Users may reside at the user sites. Their functions range from managing

tokens to providing split knowledge and dual control at all sites. Each user site

has a user information database that contains personnel information pertaining to users possessing tokens.

8.2.2. Key Management

cSOs and KTCs are the cornerstones of the ESS because they are needed to

manage cryptographic keys for the entire ESS. Key management is an essential

component of the CEFMS ESS. It provides the foundation necessary to securely

generate, store, distribute and translate cryptographic keys within CEFMS. One

of the fundamental principles for protecting keys is the practice of split knowledge

and dual control.

8.2.2.1. Key Generation

cSOs are responsible for initializing all types of tokens for all users of the ESS.

This includes cSO, dSO, SA, and User tokens. In CEFMS, tokens are used to

securely store cryptographic keys that enable the tokens to be used to initialize

cryptomodules, initiate KTCs, and allow users to access the ESS. It is important

that the cSOs who are generating the tokens maintain split knowledge and dual

control during token generation for all types of users.

8.2.2.2. Key Storage

Once keys are generated in the ESS, they must be stored securely, to prevent

unauthorized persons from accessing and using them. This is particularly critical

in a system like CEFMS because the secure key storage is necessary for

controlling financial transactions. Secure storage is needed for both the data

keys(KDs) and the key encrypting keys (*KKs). Keys are never removed from

the module without first being encrypted by some value.

8.2.2.3. Key Destruction

Key destruction involves a variety of mechanisms, including the zeroizing of keys

in a cryptomodule, the reinitialization of a token, and the removal and/or disabling

of a key in the user key database.

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8.2.3. Signature Generation and Verification

The signature generation process of the CEFMS ESS involves the calculation of

a MAC. This MAC sen/es as an electronic signature when it is created using a

notarized key. When an ESS user generates a signature on selected data, the

key used to generate the MAC is stored in encrypted form by the CEFMS

database. This key is then used in the signature verification process.

8.3. Treasury Electronic Certification System

The number one priority of the Department of the Treasury Financial

Management Service (FMS) is payment operations and the Electronic

Certification System (ECS) project is the most critical of the basic ongoing

payment operations. The ECS Project's sole purpose is to aid in achieving the

goal of ensuring a world-class delivery of all Federal government payments and

associated information to their ultimate destination.

The ECS eliminated a paper-based, error-prone and time-consuming process of

entering, certifying and making payments. The system also gives small agencies

that cannot afford mainframe computers the capability to use the Service's

Vendor Express and other Automated Clearing House (ACH) payment

processes, as well as the Same-Day-Pay-Request (Fedwire) payment process.

Formerly, only agencies that submitted magnetic tapes to the financial centers

could use the ACH payment mechanism. Paper forms were required for Same

Day Payments.

The ECS is the only method currently available for creating and processing

electronic certifications. The ECS is operating in all six Regional Financial

Centers and is used by over 500 agency end-points to prepare, certify, and

submit to the FMS an average of over 30,000 payment schedules each month.

Over 20,000 of these schedules, each month, are ones that contain both

individual payment data and the certification (Type A Schedules). These

agencies make over 75 million payments, valued at over 65 billion dollars, each

month.

Additionally, the ECS, through its use by the Federal Emergency Management

Administration (FEMA), has speeded responses to major disasters such as

hurricanes, floods, earthquakes, and other national emergencies. The ECS is now being used worldwide in 38 countries.

8.3.1. Program History

In 1986, a small staff began with an idea, a new concept. The FMS was making

payments using a very labor-intensive and time-consuming process that entailed

requiring Federal Program Agencies (FPAs) to manually submit paper SF-1 166

Voucher and Schedule of Payments (vouchers) to certify payment requests, and

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in many cases to provide payment data. These vouchers were submitted to

FMS' Regional Financial Centers by mail, express and special courier. At the

Regional Financial Centers, vouchers containing payment data were scanned

using Optical Character Recognition (OCR) equipment, which had a very high

"read" error rate. This could mean the voucher had to be returned to the agency

to be redone. The voucher would then repeat the paper-based process that is very prone to error and is time consuming. The ECS concept provided a much

faster, more efficient, more economical, and more secure method for certifying

and making payments. The ECS added electronic signatures to payment

requests submitted to FMS by FPAs. Vouchers containing certifications for

payment data submitted on magnetic tape were manually verified and used to

certify the production of payments.

The ECS electronic signature certification operation began early in 1987, with the

ECS Prototype. NIST and the General Accounting Office participated in the

approval of the concept to ensure that the system satisfied the Federal

requirements concerning voucher certification and payments. Initially, the ECS

provided the facilities to submit only schedules for small volume vendor check

payments. Subsequently, over the next 10 years, the ECS was improved and

extended through continued development to provide features that support

processing of all payment types processed by the FMS. The ECS is the only

electronic system that is available for submission and certification of payments to

the FMS. Additionally, it is the only means of timely certification for bulk payment

files telecommunicated to FMS.

8.3.2. ECS Process

The ECS provides FPAs with the ability to create, certify and transmit two

classes of payment schedules (Type A and Type B) to FMS using FMS ECS

software and Message Authentication Security hardware. Type A schedules are those that contain both the payment data for individual payments as well as the

required certification for them. Type A schedules can contain 1 to 60 payments

per schedule (average of 7.8 payments per schedule). Type B schedules are those that are used to certify payment data provided to FMS in a bulk file (through either magnetic tape or telecommunication of a bulk file). Bulk files

typically contain large numbers of payments (from hundreds to millions).

Agencies enter the schedule data on their microcomputers, a unique message

authentication code (MAC)"*^ is created using the cryptographic signature of the

agency Certifying Officer and ECS Security Administrator. The MAC is attached

to the data and transmitted to FMS' Regional Financial Center computer At the

Regional Financial Center, the MAC is recalculated, again using the

The MAC is generated on the current data and compared with the previously

generated MAC. If the two values are equal, the integrity (i.e., authenticity) of the

data is verified.

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cryptographic signatures, and is checked to see if the code is different from the

one sent to the center. If there is no difference, the payments are made;

otherwise, they are rejected.

The ECS electronic signature design uses DES, smartcard technology, a

separation-of-duties concept, and requires a dual-role-process to provide a level

of technology and security previously unemployed by government payment

processes.

8.3.3. Future Plans: Windows-Based ECS (WECS)

The electronic signature certification and MAC for payment schedules are based

upon cryptographic keys that are unique to each user of the system. The

cryptographic keys form the basis of the ECS security and integrity. The current

system of keys is based upon DES. The DES will not be supported in its current

form by NIST in the near future. Therefore, the FMS has had to look at new

technologies to provide this security and integrity function for systems where the

use of cryptography is indicated.

At this time, the most appropriate solution identified involves the use of PKI and

on-card cryptographic processors (smartcards that provide the necessary

cryptographic functions within the card), in conjunction with telecommunications

modems incorporating smartcard cryptographic functions to secure telephone

connections used to transmit data. This solution is the same one that has been

selected for the FMS Electronic Check (E-Check) project, and would strengthen

the security and integrity of the ECS, while allowing for a common cryptographic

platform and the cryptographic hardware to support any current or future

microcomputer hardware and operating system.

The pilot E-Check system will implement cryptography based on the DSS and

will include PKI cryptography. The CA, cryptographic components, and much of

the cryptographic processing and support software would be usable in a redesigned ECS. Use of the E-Check CA and cryptographic components would

reduce the cost and lead time for development of a new ECS. This would also

have the advantage of employing a common FMS cryptographic platform.

For the proposed windows-based ECS (WECS), with the use of Windows NT

(with its built-in C2 level security system) and client/server concepts, it will be

possible to make the overall security and integrity of the system much more

robust, while simplifying log-on procedures for users. Additional security and

integrity will be provided by an architecture that provides communications

encryption and authentication for all ECS electronic transmissions.

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CHAPTER 9

9. WHAT'S NEXT?

Currently available cryptographic methods provide users with valuable services.

With the constant change in computer technology, the increased internetworking

of systems, and the significant advance in computing power, new and more

powerful cryptographic methods will be needed. Following is a summary of the

new initiatives that are being evaluated by NIST.

9.1. Advanced Encryption Standard (AES)

For interoperability and other purposes, NIST strongly desires to select a single

block encryption algorithm to be specified in the AES with strength equal to or

better than that of Triple DES and significantly improved efficiency.

It is intended that the AES will specify an unclassified, publicly disclosed

encryption algorithm available royalty-free worldwide that is capable of protecting

sensitive government information well into the next century. (There is a

possibility that the AES will specify multiple algorithms.)

Encryption algorithms that have been submitted for consideration as the

Advanced Encryption Algorithm (AEA) are being reviewed by NIST and the

public on the basis of evaluation criteria. The selected AEA will be included in the FIPS for AES.

9.1.1. Minimum Acceptability Requirements

All of the candidate algorithms met the following minimum acceptability

requirements:

1 . The algorithm must implement symmetric (secret) key cryptography.

2. The algorithm must be a block cipher.

3. The candidate algorithm shall be capable of supporting key-block

combinations witii sizes of 128-128, 192-128, and 256-128 bits. A

submitted algorithm may support other key-block sizes and combinations,

and such features will be taken into consideration during analysis and

evaluation.

9.1.2. Evaluation Criteria

The following evaluation criteria are being used to review candidate algorithms.

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Security (i.e., the effort to cryptanalyze).

Cost (licensing requirements, computational efficiency, memory

requirements).

Algorithm and Implementation Characteristics (flexibility, hardware and

software suitability, simplicity).

9.1.3. AES Finalists

On August 28, 1998, NIST announced a group of fifteen AES candidate

algorithms. Members of the cryptographic community from around the world had

submitted the algorithms. Using the public comments and analyses conducted

by the global cryptographic community, NIST selected five algorithms from the

fifteen. The AES finalist candidate algorithms are MARS, RC6, Rijndael,

Serpent, and Twofish. These finalist algorithms will receive further analysis

during a second, more in-depth review period prior to the selection of the final

algorithm(s) for the AES FIPS. Following the close of the Round 2 public

analysis period, NIST intends to study all available information and propose the

AES, which will incorporate one or more AES algorithms selected from the

finalists. If all steps of the AES development process proceed as planned, it is anticipated that the standard will be completed by the summer of 2001 . Upon

publication of the standard, NIST intends to have a validation testing program in place to test the algorithm(s).

9.2. Key Agreement or Exchange

Cryptographic services depend on the secure generation and distribution of keys

(public and private). Since there is no existing FIPS in this area, a standard is needed for the design and implementation of Federal key agreement and

exchange systems. NIST has solicited public comments on potential

technologies that could be considered for a future standard for public key-based

cryptographic key agreement and exchange. NIST has specifically asked for

comments on RSA, Elliptic Curve, and Diffie-Hellman technologies. More than

one algorithm could be specified, consistent with sound security practices to give

Federal organizations more flexibility in using cryptographic systems.

9.3. Key Recovery

NIST is exploring the use of key recovery technology through a broad agency

agreement for several agency pilots and with the help of a special advisory

committee. A Key Recovery Demonstration Project has been established

involving several government agencies to demonstrate the practicality of

techniques to recover keys used in data encryption and to identify, test, and

evaluate different key recovery products and services. This effort supports an

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Administration white paper entitled Enabling Privacy, Commerce, Security, and

Public Safety in the Global Information Infrastructure.

9.4. Technical Advisory Committee

The Technical Advisory Committee to Develop a Federal Information Processing

Standard for the Federal Key Management Infrastructure (TACDFIPSFKMI) was

established by the Department of Commerce in July 1996. The Committee will advise the Secretary of Commerce on the development of a draft FIPS for the

Federal Key Management Infrastructure. The purpose of the standard is to

specify requirements for key recovery components, and to enable the validation

of components claiming conformance. The standard encompasses the security

(from an implementation, managerial and operation perspective) and the

availability of key recovery components, as well as defining interoperability

requirements.

Key recovery is motivated by three primary scenarios:

1 . Recovery of stored data on behalf of an organization (or individual) e.g., in response to accidental loss of keys;

2. Recovery of stored or communicated data on behalf of an organization

(e.g., for the purposes of monitoring or auditing activities); and

3. Recovery of communicated or stored data by lawfully authorized

authorities.

The first scenario supports the ability to regain access to data that would

otherwise be lost. The second scenario encompasses internal investigation

authorized by an organization. The final scenario encompasses data acquired

under the authorization of court orders for wiretaps, search and seizure orders,

civil suit subpoenas, etc. A Key Recovery System (KRS) manages cryptographic keys in support of data

recovery when normal key access mechanisms fail. These systems must be

carefully designed so that plaintext may be recovered in a timely manner, and so

that only authorized recoveries are permitted. Therefore, security is a critical

factor in any KRS design.

9.5. FIPS 140-2

FIPS 140-1 , first published in 1994, specified that it be reviewed within five years.

In 1998, NIST solicited public comments on reaffirming the standard. The

comments received by NIST supported maintaining the standard. The comments

also supported updating the standard due to advances in technology. The

proposed revision (FIPS 140-2) is currently being prepared.

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APPENDIX A

ACRONYMS

ACC Application Cryptographic Commands

ACH Automated Clearing House

AEA Advanced Encryption Algorithm

A (— O AES Advanced Encryption Standard

ANSI Amencan National Standards Institute

API Application Programming Interface

BCA Bridge Certification Authority

CA Certification Authority

CAPI Cryptographic Application Programming Interface

CBC Cipher Block Chaining Mode

CC Common Criteria

CEFMS Corps of Engineers Financial Management System

CFB Cipher Feedback Mode

cKMF central Key Management Facility

CKMS Centralized Key Management System

cKTC central Key Translation Center

CM Configuration Management

CMT Cryptographic Module Testing

CMV Cryptographic Module Validation

CMVP Cryptographic Module Validation Program

COTS Commercial-Off-The-Shelf

CPS Certification Practice Statement

CRADA Cooperative Research and Development Agreement

CRL Certificate Revocation List

CSA Computer Security Act

CSC Cryptographic Service Call

CSE I 1 1 * 1 I Communications Security Establishment

cSO central Security Officer

CSPs Critical Security Parameters

CSR Certificate Status Responder

DAA A J. 1 X* X* A 1 *xl Data Authentication Algorithm

DAC Data Authentication Code

DEA Data Encryption Algorithm

DES Data Encryption Standard

DID Data Item Identifier

Oil Defense Information Infrastructure

DISN Defense Information Systems Network

DOE Department of Energy

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DOT Department of Transportation

DPMA Domain Policy Management Authority

DSA Digital Signature Algorithm

dSO district Security Officer

DSS Digital Signature Standard

DSSV Digital Signature Storage and Verification

DTR Derived Test Requirement

EAL Evaluation Assurance Level

EC Elliptic Curve

ECB Electronic Codebook Mode

ECDSA Elliptic Curve Digital Signature Algorithm

ECS Electronic Check System

EDI Electronic Data Interchange

I— r-r-\ EFP Environmental Failure Protection

EFT Environmental Failure Testing

EGS Electronic Grants System

EMI/EMC Electromagnetic Interference/Electromagnetic Compatibility

ESS Electronic Signature System

FCC Federal Communications Commission

FEMA Federal Emergency Management Administration

FIPS Federal Information Processing Standard

FIPS PUB Federal Information Processing Standard Publication

FMS Financial Management Service

FPA Federal Program Agencies

FPMA Federal Policy Management Authority

GAO General Accounting Office

GCS-API Generic Cryptographic Services - API

GUI Graphical User Interface

l&A Identification and Authentication

IEEE Institute of Electrical and Electronics Engineers

IETF Internet Engineering Task Force

IT Information Technology

ISO International Organization for Standardization

IV Initialization Vector

IV&V Independent Verification and Validation

*KK Key Encrypting Key

KKcms Central Master Storage Key Encrypting Key

KAT Known Answer Test

KDcom Data Communications Data Key

KEA Key Exchange Algorithm

KMF Key Management Facility

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KR Key Recovery

KRA Key Recovery Agent

KRC Key Recovery Center

KHUr r\ey Hecovery uemonstration rroject

KRS Key Recovery System

KTC Key Translation Center

LDAP Lightweight Directory Access Protocol

MAO Message Authentication Code

MCT Monte Carlo Tests

MID Message Identifier

MISPC Minimum Interoperability Specification for PKI Components

MCT Monte Carlo Test

NIAP National Information Assurance Partnership

Mil

INI! iNaiionai inTormaiion inirasiruciure

NIST National Institute of Standards and Technology

NSA National Security Agency

NTIS National Technical Information Service

M\/l AD rNationai voluntary LaDoraiory Accreaiiation rrogram

OCR Optical Character Recognition

OFB Output Feedback Mode

0MB Office of Management and Budget

PC Personal Computer

PCA Policy Certification Authority

r~) 1 K

1

PIN Personal Identification Number

PKI Public Key Infrastructure

POC Point-of-Contact

PR Protection Profile

PRNG PseudoRandom Number Generator

RA Registration Authority

RFP Request for Proposal

RNG Random Number Generator

SA Security Administrator

O LI A bHA becure riasn Aigoritnm

SHS Secure Hash Standard

SP Special Publication

SSL Secure Socket Layer

SUT System Under Test

TCBC TDEA Cipher Block Chaining Mode

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TCBC-I IDEA Cipher Block Chaining Mode - Interleaved

IDEA Triple DEA

TECB IDEA Electronic Codebook Mode

TCFB IDEA Cipher Feedback Mode

TCFB-P TDEA Cipher Feedback Mode - Pipelined

1 Ub Target of Evaluation

TOFB TDEA Output Feedback Mode

TOFB-I TDEA Output Feedback Mode - Interleaved

TSF TOE Security Functions

TSP TOE Security Policy

U.S. United States

USEGS U.S. Electronic Grants System

WAN Wide Area Network

WECS Windows-based ECS

WWW World Wide Web

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APPENDIX B

TERMS AND DEFINITIONS

This section includes terms and definitions that are commonly used in or associated with cryptography. In general, the definitions are drawn from FIPS

PUBs, related documents, and other standards. The source of each definition is included with the definition and the full references are included in Appendix C.

The source is listed at the end of the definition in square brackets [ ]. Some

terms include more than one definition - multiple definitions are included to

illustrate the variations in the use of a term or to provide a more detailed

definition.

Application Programming Interface (API): The interface between the

application software and the application platform, across which all services are provided. The API is primarily in support of application portability, but

system and application interoperability is also supported by a communication

API. [X/Open Preliminary Specification]

asset: Information resources that support an organization's mission.

[NIST Special Publication (SP) 800-12]

Information or resources to be protected by the countermeasures of a Target

of Evaluation (TOE). [Common Criteria]

asymmetric algorithm: See public-key algorithm.

authentication: The broadest definition of authentication within computing

systems encompasses identity verification, message origin authentication,

and message content authentication. [FIPS PUB 190]

Authenticity refers to validating the source of a message i.e., that it was

transmitted by a properly identified sender and is not a replay of a previously

transmitted message. [NIST SP 800-2]

automated key distribution: The distribution of cryptographic keys, usually in encrypted form, using electronic means, such as a computer network.

[FIPS PUB 140-1]

binding: An acknowledgment by a trusted third party that associates an entity's

identity with its public key. This may take place through (1) a certification

authority's generation of a public key certificate, (2) a security officer's

verification of an entity's credentials and placement of the entity's public key

and identifier in a secure database, or (3) an analogous method.

[FIPS PUB 196]

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certificate (or public key certificate): A digitally signed data structure defined in the X.509 standard that binds the identity of a certificate holder (or subject) to

a public key. [MISPC]

certificate revocation list (CRL): a list of revoked but unexpired certificates

issued by a CA. [MISPC]

certification authority (CA): A trusted entity that issues certificates to end

entities and other CAs. CAs issue CRLs periodically, and post certificates

and CRLs to a repository. [MISPC]

certification path: An ordered sequence of certificates, leading from a certificate

whose public key is known by a client, to a certificate whose public key is to

be validated by the client. [MISPC]

ciphertext: Encrypted (enciphered) data. [FIPS PUB 46-3]

claimant: An entity which is or represents a principal for the purposes of

authentication, together with the functions involved in an authentication

exchange on behalf of that entity. A claimant acting on behalf of a principal

must include the functions necessary for engaging in an authentication

exchange (e.g., a smartcard (claimant) can act on behalf of a human user

(principal)). [FIPS PUB 196]

compromise: The unauthorized disclosure, modification, substitution or use of

sensitive data (including plaintext cryptographic keys and other critical

security parameters). [FIPS PUB 190]

confidentiality: The property that sensitive information is not disclosed to

unauthorized individuals, entities or processes. [FIPS PUB 140-1]

countermeasure: Any action, device, procedure, technique, or other measure

that reduces a system's vulnerability to a threat. [NIST SP 800-12]

critical security parameters: Security-related information (e.g., cryptographic

keys, authentication data such as passwords and PINs) appearing in plaintext or othen/vise unprotected form and whose disclosure or modification can

compromise the security of a cryptographic module or the security of the

information protected by the module. [FIPS PUB 140-1]

cryptographic hash function: A (mathematical) function that maps values from

a large (possibly very large) domain into a smaller range. The function

satisfies the following properties:

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1 . (One-way) It is computationally infeasible to find any input which maps to

any pre-specified output;

2. (Collision free) It is computationally infeasible to find any two distinct

inputs that map to the same output. [ANSI X9.42]

cryptographic key: A parameter used in conjunction with a cryptographic

algorithm that determines:

- the transformation of plaintext data into ciphertext data,

- the transformation of ciphertext data into plaintext data,

- a digital signature computed from data,

- the verification of a digital signature computed from data, or

- a data authentication code (DAC) computed from data.

[FIPS PUB 140-1]

cryptographic key component: A parameter which is combined (e.g., via a bit- wise exclusive-OR operation) with one or more other identically sized key

component(s) to form a plaintext cryptographic key. [FIPS PUB 140-1]

cryptographic module: The set of hardware, software, firmware, or some

combination thereof that implements cryptographic logic or processes,

including cryptographic algorithms, and is contained within the cryptographic

boundary of the module. [FIPS PUB 140-1]

cryptography: The discipline which embodies principles, means and methods

for the transformation of data to hide its information content, prevent its undetected modification, prevent its unauthorized use or a combination

thereof. [ANSI X9.31]

Cryptography deals with the transformation of ordinary text (plaintext) into

coded form (ciphertext) by encryption and transformation of ciphertext into

plaintext by decryption. [NIST SP 800-2]

cryptoperiod: The time span during which a specific key is authorized for use or

in which the keys for a given system may remain in effect. [ANSI X9.31]

Data Authentication Code (DAC): Applying the Data Authentication Algorithm

(DAA) to data generates a DAC. The DAC is a mathematical function of both

the data and a cryptographic key. When the integrity of the data is to be

verified, the DAC is generated on the current data and compared with the

previously generated DAC. If the two values are equal, the integrity (i.e.,

authenticity) of the data is verified. [FIPS PUB 113]

A DAC is also known as a Message Authentication Code (MAC) in ANSI

standards. [FIPS PUB 140-1]

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data integrity: The state that exists when computerized data is the same as that

in the source documents and has not been exposed to accidental or malicious

alteration or destruction. [FIPS PUB 39]

data l<ey: A cryptographic key which is used to cryptographically process data

(e.g., encrypt, decrypt, authenticate). [FIPS PUB 140-1]

decryption: The process of changing ciphertext into plaintext. [FIPS PUB 81]

DES: The symmetric encryption algorithm defined by the Data Encryption

Standard (FIPS PUB 46-3). [MISPC]

DES IVIAC: An algorithm for generating a message authentication code (MAC)

using the symmetric encryption algorithm DES. [MISPC]

digital signature: The result of a cryptographic transformation of data which,

when properly implemented, provides the services of: 1. origin authentication,

2. data integrity, and

3. signer non-repudiation. [ANSIX9.31]

The digital signature is computed using a set of rules (e.g., the Digital

Signature Algorithm (DSA)) and a set of parameters such that the identity of

the signatory and integrity of the data can be verified. [FIPS PUB 186-2]

A data unit that allows a recipient of a message to verify the identity of the

signatory and integrity of the message. [MISPC]

A nonforgeable transformation of data that allows the proof of the source (with

non-repudiation) and the verification of the integrity of that data.

[FIPS PUB 196]

Digital Signature Algorithm (DSA): The DSA is used by a signatory \o generate

a digital signature on data and by a verifier \o verify the authenticity of the

signature. [FIPS PUB 186-2]

dual control: A process of utilizing two or more separate entities (usually

persons) operating in concert, to protect sensitive functions or information.

[ANSI X9.17]

electronic signature: A method of signing an electronic message that—

(A) Identifies and authenticates a particular person as the source of the

electronic message; and

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(B) Indicates such person's approval of the information contained in the

electronic message. [GPEA]

Elliptic Curve Digital Signature Algorithm (ECDSA): A digital signature

algorithm that is an analog of DSA using elliptic curve mathematics and

specified in ANSI standard X9.62. [MISPC]

encrypted Icey (ciphertext key): A cryptographic key that has been encrypted

with a key encrypting key, a PIN or a password to disguise the value of the

underlying plaintext key. [FIPS PUB 140-1]

encryption: The process of changing plaintext into ciphertext for the purpose of

security or privacy. [FIPS PUB 81]

entity: Any participant in an authentication exchange such a participant may be

human or non-human, and may take the role of a claimant and/or verifier.

[FIPS PUB 196]

ephemeral data: In ANSI X9.42, ephemeral data is data specific to a particular

execution of a cryptographic scheme. Ephemeral data includes ephemeral

private/public keys and may include ephemeral-key domain parameters.

[ANSI X9.42]

error detection code: A code computed from data and comprised of redundant

bits of information designed to detect, but not correct, unintentional changes

in the data. [FIPS PUB 140-1]

FIRS approved security method: A security method (e.g., cryptographic

algorithm, random number generator) that is either a) specified in a FIPS, or

b) adopted in a FIPS and specified either in an appendix to the FIPS or in a

document referenced by the FIPS. [FIPS PUB 196]

hash: The SHA-1 produces a 160-bit condensed representation of the message

called a message digest. The message digest is used during generation of a

signature for the message. The SHA-1 is also used to compute a message

digest for the received version of the message during the process of verifying

the signature. Any change to the message in transit will, with very high

probability, result in a different message digest, and the signature will fail to

verify. [FIPS PUB180-1]

hash code: The string of bits that is the output of a hash function. [MISPC]

initialization vector (IV): A vector used in defining the starting point of an

encryption process within a cryptographic algorithm. [FIPS PUB 140-1]

123
Implementing Cryptography

integrity: The property that sensitive data has not been modified or deleted in an unauthorized and undetected manner. [FIPS PUB 140-1]

Integrity refers to assurance that a message was not modified accidentally or

deliberately in transit, by replacement, insertion or deletion.

[NIST SP 800-2]

key: See cryptographic key

key encrypting key: A cryptographic key that is used for the encryption or decryption of other keys. [FIPS PUB 140-1]

key management: The activities involving the handling of cryptographic keys

and other related security parameters (e.g., IVs, counters) during the entire

life cycle of the keys, including the generation, storage, distribution, entry and

use, deletion or destruction, and archiving. [FIPS PUB 140-1]

The generation, storage, secure distribution and application of keying material

in accordance with a security policy that prevents its modification,

unauthorized use, or a combination thereof. [ANSI X9.42]

keying material: The data (e.g., keys and IVs) necessary to establish and

maintain cryptographic keying relationships. [ANSI X9. 17]

message: The data to be signed. [ANSI X9.31]

message identifier {M\D): A field that may be used to identify a message.

Typically, this field is a sequence number. [ANSI X9.31]

message authentication code (IVIAC): A data authenticator generated from

the message, usually through cryptographic techniques. In general, a

cryptographic key is also required as input. [MISPC]

Note: the MAC as specified in ANSI X9.9 is computed in the same manner as

the DAC specified in FIPS PUB 1 13.

message digest: The fixed size result of hashing a message. [MISPC]

non-repudiation: This service provides proof of the integrity and origin of data

that can be verified by a third party. [ANSI X9.31]

Non-repudiation of origin is protection against a sender of a message later

denying transmission. [NIST SP 800-2]

password: A string of characters used to authenticate an identity or to verify

access authorization. [FIPS PUB 140-1]

124
Implementing Cryptography

Personal Identification Number (PIN): A 4 to 12 character alphanumeric code

or password used to authenticate an identity, commonly used in banking

applications. [FIRS PUB 140-1]

plaintext: Unencrypted (unenciphered) data. [FIRS RUB 81]

principal: An entity whose identity can be authenticated. [FIRS RUB 196]

private key: A cryptographic key used with a public key cryptographic algorithm,

uniquely associated with an entity, and not made public. [FIRS RUB 140-1]

In an asymmetric (public) key cryptosystem, the key of an entity's key pair

that is known only by that entity. A private key may be used to:

(1) Compute the corresponding public key,

(2) Make a digital signature that may be verified by the corresponding

public signature,

(3) Decrypt data encrypted by the corresponding public key, or

(4) Compute a piece of common shared secret information together with

other information.

[ANSI X9.42]

The private key is used to generate a digital signature. This key is mathematically linked with a corresponding public key. [FIRS RUB 196]

public key: A cryptographic key used with a public key cryptographic algorithm,

uniquely associated with an entity, and which may be made public. [FIRS

RUB 140-1]

In an asymmetric (public) key cryptosystem that key of an entity's key pair

that may be publicly known. A public key may be used to:

(1) Verify a digital signature that is signed by the corresponding private

key,

(2) Encrypt data that may be decrypted by the corresponding private key,

(3) Compute a piece of shared information by other parties.

[ANSI X9.42]

125
Implementing Cryptography

The public key is used to verify a digital signature. This key is mathematically

linked with a corresponding private key. [FIPS PUB 196]

public key certificate (certificate): A set of data that unambiguously identifies

an entity, contains the entity's public key, and is digitally signed by a trusted

third party (certification authority). [FIPS PUB 196]

public key cryptography (reversible): Reversible public key cryptography is an

asymmetric cryptographic algorithm where data encrypted using the public

key can only be decrypted using the private key and conversely, data

encrypted using the private key can only be decrypted using the public key.

[ANSIX9.31]

public key (asymmetric) cryptographic algorithm: A cryptographic algorithm

that uses two related keys, a public key and a private key; the two keys have

the property that, given the public key, it is computationally infeasible to

derive the private key. [FIPS PUB 140-1]

These algorithms are referred to as "asymmetric" because they rely on two

different keys to perform cryptographic processing of data. [FIPS PUB 190]

public key infrastructure (PKI): An architecture which is used to bind public

keys to entities, enable other entities to verify public key bindings, revoke

such bindings, and provide other services critical to managing public keys.

[FIPS PUB 196]

role: A predefined set of rules establishing the allowed interactions between a

user and the TOE. [Common Criteria]

RSA: A public-key signature algorithm specified in the RSA Encryption Standard,

Version 1.4, RSA Data Security, Inc., 3 June 1991.

secrecy: Secrecy refers to denial of access to information by unauthorized

individuals. [NIST SP 800-2]

secret key: A cryptographic key used with a secret key cryptographic algorithm,

uniquely associated with one or more entities, and which shall not be made

public. The use of the term "secret" in this context does not imply a

classification level, rather the term implies the need to protect the key from

disclosure or substitution. [FIPS PUB 140-1]

secret key (symmetric) cryptographic algorithm: A cryptographic algorithm

that uses a single, secret key for both encryption and decryption.

[FIPS PUB 140-1]

126
Implementing Cryptography

secure hash algorithm: An algorithm that can generate a condensed message

representation of a message or a data file, called a message digest.

[FIPS PUB 190]

session key: The cryptographic key used by a device [module] to encrypt and

decrypt data during a session. [FIPS PUB 185]

signature generation: Makes use of a private key to generate a digital

signature. Only the possessor of the user's private key can perform signature

generation. [FIPS PUB 186-2]

signature verification: Makes use of a public key that corresponds to, but is not

the same as, the private key. Anyone can verify the signature of a user by

employing that user's public key. [FIPS PUB 186-2]

split knowledge: A condition under which two or more entities separately have

key components which individually convey no knowledge of the plaintext key

which will be produced when the key components are combined in the

cryptographic module. [FIPS PUB 140-1]

Note: in more general terms, split knowledge applies to splitting knowledge of

the secret S among two or more individuals.

static data: Data that is relatively long-lived. In ANSI X9.42, static data is data

common to a number of executions of a cryptographic scheme. Static data

includes static-key domain parameters and static private/public keys.

[ANSI X9.42]

symmetric key: A cryptographic key that is used in symmetric cryptographic

algorithms. The same symmetric key that is used for encryption is also used

for decryption. [ANSI X9.42]

threat: An entity or event with the potential to harm a system.

[NISTSP 800-12]

trusted path: A mechanism by which a person or process can communicate

directly with a cryptographic module and which can only be activated by the

person, process or module, and cannot be imitated by untrusted software

within the module. [FIPS PUB 140-1]

A means by which a user and a Target of Evaluation Security Functions

(TSF) can communicate with necessary confidence to support the Target of

Evaluation Security Policy (TSP). [Common Criteria]

127
Implementing Cryptography

verifier: An entity that is or represents the entity requiring an authenticated

identity. A verifier includes the functions necessary for engaging in authentication exchanges. [FIPS PUB 196]

vulnerability: A condition or weakness in (or absence of) security procedures,

technical controls, physical controls, or other controls that could be exploited

by a threat. [NIST SP 800-12]

zeroization/zeroisation: A method of erasing electronically stored data by

altering the contents of the data storage so as to prevent the recovery of the

data. [FIPS PUB 140-1]

128
Implementing Cryptography

APPENDIX C

REFERENCE LIST

American Bankers Association, American National Standard for Financial

Institution Key Management (Wholesale), ANSI X9. 1 7-1 995, Washington, DC,

1995.

American Bankers Association, American National Standard for Financial

Institution Message Authentication, ANSI X9. 9-1 986 (R1994), Washington, DC,

Approved August 15, 1986, (Revised, 1994).

American Bankers Association, Digital Signatures using Reversible Public Key

Cryptography for the Financial Sen/ices Industry (rDSA)), ANSI X9.31 -1 998,

Washington, DC, 1998.

American Bankers Association, Key Agreement and Key Transport Using Elliptic

Cun/e-Based Cryptography, Working Draft ANSI X9.63,1997.

American Bankers Association, Modes of Operation Validation System for the

Triple Data Encryption Algorithm (TMOVS): Requirements and Procedures, ANSI

TG-19, Washington, DC, 1999.

American Bankers Association, Public Key Cryptography for the Financial

Services Industry: Agreement of Symmetric Keys Using Discrete Logarithm

Cryptography, Working Draft ANSI X9.42-2000.

American Bankers Association, Public Key Cryptography for the Financial

Services Industry: The Elliptic Curve Digital Signature Algorithm, ANSI X9.62-

1998.

American Bankers Association, Public Key Cryptography Using Irreversible

Algorithms for the Financial Services Industry, Part 1 : The Digital Signature

Algorithm (DSA), ANSI X9.30-1 997.

American Bankers Association, Public Key Cryptography Using Irreversible

Algorithms for the Financial Services Industry: The Secure Hash Algorithm (SHA1) (Revised), ANSI X9.30-1993, Part 2.

American Bankers Association, The Transport of Symmetric Algorithms Keys

Using Reversible Public Key Cryptography, Working DRAFT ANSI X9.44-1998.

American Bankers Association, Triple Data Encryption Algorithm Modes of

Operation, ANSI X9.52-1998, Washington, DC, 1998.

129
Implementing Cryptography

Burr, William E., Public Key Infrastructure (PKI) Version 1 Technical

Specifications - Part C: Concept of Operations, Federal PKI Technical Working

Group, Nov. 16, 1995.

Burr, William, Donna Dodson, Noel Nazario, W. Timothy Polk, Mininrium

Interoperability Specification for PKI Components, Version 1, Special Publication

800-15, Gaithersburg, MD, National Institute of Standards and Technology,

January 1998.

Common Criteria for Information Technology Security Evaluation, Version 2.0,

May 1998, International Standard ISO/IEC 15408 Evaluation Criteria for

Information Technology Security, ISO/IEC JTC1 and Common Criteria

Implementation Board.

Computer Security Act of 1987, 40 U.S. Code 759, (Public Law 100-235), 8

January 1988.

Department of Defense, Department of Defense Trusted Computer System

Evaluation Criteria, DOD 5200.28-STD, December 1985.

Diffie, W. and M.E. Hellman, "New Directions in Cryptography," IEEE

Transactions on Information Theory, v. IT-22, n. 6, Nov. 1976, pp. 644-654.

Dodson, D., Keller, S. S., Chang, S., and Smid. M. E., Technical Component for

the CEFI^S Electronic Signature System RFP, NIST September 22, 1 992.

Foti, J., Keller, S., and Dodson, Donna, Security Review of the CEFMS

Electronic Signature System, NIST, May 17, 1996.

General Accounting Office (GAO), Corps of Engineers Electronic Signature

System, GAO/AIMD-97-18R, November 19, 1996.

Government Papen/vork Elimination Act (GPEA), Title XVII of Public Law 105-

277, October 21, 1998.

Guttman, Barbara, Computer Security Considerations in Federal Procurements:

A Guide for Procurement Initiators, Contracting Officers, and Computer Security

Officials, Special Publication 800-4, Gaithersburg, MD, National Institute of

Standards and Technology, March 1992.

Guttman, Barbara and Edward Roback, An Introduction to Computer Security:

The NIST Handbook, Special Publication 800-12, Gaithersburg, MD, National

Institute of Standards and Technology, February 6, 1996.

130
Implementing Cryptography

Keller, Sharon and Miles Smid, Modes of Operation Validation System (IVIOVS):

Requirements and Procedures, Special Publication 800-17, Gaithersburg, MD,

National Institute of Standards and Technology, February 1998.

MacLean, Abby, EZ_ERA32 and the Key Recovery Demonstration Project

(KRDP), Office of Energy Research, Department of Energy, 1998.

Menezes, Alfred J., vanOorschot, Paul C, and Vanstone, Scott A., Handbook of

Applied Cryptography, CRC Press, Inc., New York, 1997.

MITRE Corporation, Public Key Infrastructure Study, Final Report, National

Institute of Standards and Technology, April 1994.

Myers, M, R. Ankney, A. Malpani, S. Galperin, and C. Adams, Internet Public key

Infrastructure Online Certificate Status Protocol - OSCP, draft, Sept. 1998.

National Institute of Standards and Technology, Advanced Authentication

Technology, NIST ITL Bulletin, 1991-12.

National Institute of Standards and Technology, Advanced Encryption Standard,

NIST ITL Bulletin, 1997-02.

National Institute of Standards and Technology, Computer Data Authentication,

Federal Information Processing Standards Publication 113, May 30, 1985.

National Institute of Standards and Technology, Computer Security Publications,

NIST Publication List 91, Revised October 1999.

National Institute of Standards and Technology, Cryptographic Standards and

Supporting Infrastructures: A Status Report, NIST ITL Bulletin, 1997-09.

National Institute of Standards and Technology, Data Encryption Standard,

Federal Information Processing Standards Publication 46-2, December 30, 1993.

National Institute of Standards and Technology, DES Modes of Operation,

Federal Information Processing Standards Publication 81, December 2, 1980.

National Institute of Standards and Technology, Digital Signature Standard

(DSS), Federal Information Processing Standards Publication 186, May 19,

1994.

National Institute of Standards and Technology, Digital Signature Standard, NIST

ITL Bulletin, 1994-12.

National Institute of Standards and Technology, Digital Signature Standard

Validation System (DSSVS) User's Guide, June 20, 1997.

131
Implementing Cryptography

National Institute of Standards and Technology, Entity Authentication Using

Public Key Cryptographiy, Federal Information Processing Standards Publication

196, February 18, 1997.

National Institute of Standards and Technology, Escrowed Encryption Standard

(EES), Federal Information Processing Standards Publication 185, February

1994.

National Institute of Standards and Technology, A Frameworf< for Cryptographic

Standards, NIST ITL Bulletin, 1995-08.

National Institute of Standards and Technology, Guideline for the Use of

Advanced Authentication Technology Alternatives, Federal Information

Processing Standards Publication 190, September 28, 1994.

National Institute of Standards and Technology, Implementation Issues for

Cryptography, NIST ITL Bulletin, 1996-08.

National Institute of Standards and Technology, Key Management Using ANSI

X9. 17, Federal Information Processing Standards Publication 171 , April 27,

1992.

National Institute of Standards and Technology, Public Key Infrastructure

Technology, NIST ITL Bulletin, 1997-07.

National Institute of Standards and Technology, Secure Hash Standard, Federal

Information Processing Standards Publication 180-1, April 17, 1995.

National Institute of Standards and Technology, Security Requirements for

Cryptographic Modules, Federal Information Processing Standards Publication

140-1, January 11, 1994.

National Security Agency (NSA), Security Service API: Cryptographic API

Recommendation Second Edition, NSA Cross Organization CAPI Team, July 1,

1996.

National Security Telecommunications and Information Systems Security

Committee, National Information Systems Security Glossary, NSTISSI No. 4009,

5 June 1992.

Nechvatal, James, Public-Key Cryptography, Special Publication 800-2,

Gaithersburg, MD, National Institute of Standards and Technology, April 1991.

132
Implementing Cryptography

Office of Management and Budget, Guidance for Preparation of Security Plans

for Federai Computer Systems Tfiat Contain Sensitive Information, 0MB Bulletin

No. 90-08, 9 July 1990.

Office of Management and Budget, Security of Federal Automated Information

Resources, Appendix III to 0MB Circular No. A-130, February 8, 1996.

RSA Laboratories, Diffie-Hellman Key-Agreement Standard, Technical Note

Version 1.4, PKCS #3, November 1, 1993.

Schneier, Bruce, Applied Cryptography, Second Edition, John Wiley & Sons, Inc.,

New York, c. 1996.

Smith, B. H., Secure Electronic Grants: Key Recovery Demonstration Project

Phase I Accomplishments, Test Results and Remaining Tasks, U.S. Department

of Transportation, July 24, 1998.

Swanson, Marianne and Barbara Guttman, Generally Accepted Principles and

Practices for Securing Information Technology Systems, Special Publication 800-

14, Gaithersburg, MD, National Institute of Standards and Technology,

September 20, 1995.

X/Open, X/Open Preliminary Specification: Generic Cryptographic Service API,

draft 8, April 20, 1996.

West, John P., Electronic Certification System (ECS) Development and

Enhancement, Financial Management Sen/ice, Department of the Treasury, April

8, 1998.

West, John P. and Chris Shanefelter, Decision Fact Sheet, Electronic

Certification System (ECS), Financial Management Service, Department of the

Treasury, March 18, 1998.

For sale by the U.S. Government Printing Office Superintendent of Documents, Mail Stop: SSOP, Washington, DC 20402-9328 ISBN 0-16-050241-1

133

^US. GOVERNMENT PRINTING OmCE: 1999 - 4S0-T4«1711«
i

ISBN 0-16-050241-1

9 780 60"502415

90000
Technical Publications

Periodical

Journal of Research of the National Institute of Standards and Technology—Reports NIST research and

development in those disciplines of the physical and engineering sciences in which the Institute is active. These include physics, chemistry, engineering, mathematics, and computer sciences. Papers cover a broad

range of subjects, with major emphasis on measurement methodology and the basic technology underlying

standardization. Also included from time to time are survey articles on topics closely related to the Institute's technical and scientific programs. Issued six times a year.

Nonperiodicals

Monographs—Major contributions to the technical literature on various subjects related to the Institute's scientific and technical activities. Handboolcs—Recommended codes of engineering and industrial practice (including safety codes) developed

in cooperation with interested industries, professional organizations, and regulatory bodies.

Special Publications—Include proceedings of conferences sponsored by NIST, NIST annual reports, and

other special publications appropriate to this grouping such as wall charts, pocket cards, and bibliographies.

National Standard Reference Data Series—Provides quantitative data on the physical and chemical

properties of materials, compiled from the world's literature and critically evaluated. Developed under a

worldwide program coordinated by NIST under the authority of the National Standard Data Act (Public Law

90-396). NOTE: The Journal of Physical and Chemical Reference Data (JPCRD) is published bi-monthly for NIST by the American Chemical Society (ACS) and the American Institute of Physics (AlP). Subscriptions,

reprints, and supplements are available from ACS, 1155 Sixteenth St., NW, Washington, DC 20056.

Building Science Series—Disseminates technical information developed at the Institute on building

materials, components, systems, and whole structures. The series presents research results, test methods,

and performance criteria related to the structural and environmental functions and the durability and safety

characteristics of building elements and systems.

Technical Notes—Studies or reports which are complete in themselves but restrictive in their treatment of a

subject. Analogous to monographs but not so comprehensive in scope or definitive in treatment of the

subject area. Often serve as a vehicle for final reports of work performed at NIST under the sponsorship of other government agencies.

Voluntary Product Standards—Developed under procedures published by the Department of Commerce in Part 10, Title 15, of the Code of Federal Regulations. The standards establish nationally recognized

requirements for products, and provide all concerned interests with a basis for common understanding of the

characteristics of the products. NIST administers this program in support of the efforts of private-sector

standardizing organizations.

Order the following NIST publications—FIPS and NISTIRs—from the National Technical

Information Sen/ice, Springfield, VA 22161.

Federal Information Processing Standards Publications (FIPS PUB)—Publications in this series collectively constitute the Federal Information Processing Standards Register. The Register serves as the official source

of information in the Federal Government regarding standards issued by NIST pursuant to the Federal Property and Administrative Services Act of 1949 as amended. Public Law 89-306 (79 Stat. 1 127), and as implemented by Executive Order 11717 (38 FR 12315, dated May 11, 1973) and Part 6 of Title 15 CFR

(Code of Federal Regulations).

NIST Interagency Reports (NISTIR)—A special series of interim or final reports on work performed by NIST

for outside sponsors (both government and nongovernment). In general, initial distribution is handled by the sponsor; public distribution is by the National Technical Information Service, Springfield, VA 22161, in paper

copy or microfiche form.
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